With the necromancer patch I believe a fair number of old players perhaps from a really long time ago (Maybe even pre-ROS) have rejoined to try out the new content.
Although necromancer is the main focus of this patch, in the 2+ years that some of us have been gone, a good number of changes and updates have been made that provide more stuff to play (well, grind).
My guide is mainly for PC players, and will cover major changes made from ROS all the way to the current patch, and is focused around players who didn't play ROS, and players who quit up to the Season 3 era (prior to the addition of Kanai's Cube)
You will NOT find itemization guides here, as the main purpose is to keep old players up to scratch on systemic changes and help them to understand the current meta. Please visit the individual class subreddits for that purpose by going to </r/diablo3CLASSNAME>
In order of historical changes, this is a summary of content and patches since D3V2. Do skip what you already know about if you need to, or it might get repetitive!
Players from Base Game / Pre-ROS Expansion
For those who came here before ROS, more or less ROS is the biggest content patch for Diablo 3, changing much of the playstyle. Biggest factors include an increase in level cap from 60 to 70, a new Act 5 in the storyline, as well as Adventure mode which featured Bounty Hunting and Rift content. Difficulty levels also increased above the default base difficulties, with Torment 1 to Torment 6 becoming available
Bounties were set tasks in the world which were marked on the world map. Players would have to visit the locations and complete tasks, usually about killing a specific elite monster or a boss, and would earn exp and gold for it. Finishing all bounties in an Act would earn them a treasure box, with loot in it – the loot was later patched to drop important Cache Materials (elaborated on later under the Kanai's Cube section)
Rifts were instanced dungeons that are randomly generated with enemies to fight. The goal is to summon a rift guardian by killing monsters until a progress bar is full, and then defeating the said rift guardian.
Removal of Auction House
Lastly, a week before release of ROS, the Auction House was removed, and players could no longer trade or sell items to each other, with legendaries being bound to their accounts. The only way to trade items now is to play in the same instance as friends, and legendaries looted during the session can be traded to those friends with a time limit (around 3 hours).
A good way to catch up to ROS content and enjoy the new stories added would be to play through the entire campaign again on a new character, as many skills were revamped and there is a lot of content to explore.
An NPC known as Kadala was also added, which allows players to earn Blood Shards from various means that could be gambled for a random item (including possible legendaries) for a specific slot.
Post ROS: Greater Rift Content and Seasons
The current meta for progression in Diablo 3 is through a special type of Rift Dungeon known as a Greater Rift, which scales in numerals from Level 1 all the way to as high as players are able to clear. It is identical to Nephalem Rifts except that enemies do not drop items, and skills are locked upon entry. Completion via killing the final Rift Guardian boss is the only way to obtain any reward. The clears are timed; however, failing the time period does not mean that there will not be any reward – killing the Rift Guardian still causes a number of guaranteed legendary drops that increase with GR Level.
The main initial reward for completing Greater Rifts are Legendary Gemstones, which can be socketed into Amulet or Rings to get powerful modifiers. Clearing Greater Rifts within the time period unlocks access to Urshi, an NPC that is able to upgrade the above mentioned Legendary Gemstones and have them increase in Rank.
Seasons and Leaderboards System
With Greater Rifts also came the introduction of the Seasons system, which allowed Seasonal characters to be created that had access to exclusive legendaries in Season Play. It is identical to the normal mode, but with Paragon levels fresh for new characters, a separate stash, and at the end of a season the characters transferred over into the normal modes (with stash items being sent via mailbox) The purpose for Seasons was to allow a form of competitive play between players, with Greater Rift scores being used to place them on a leaderboard that is visible to all players on the Leaderboards page.
Note: Greater Rifts are not affected by the difficulty setting of the current instance.
Season 4: Ancient Legendaries
Around Season 4 (Patch 2.1.2) legendaries were updated to have a chance to roll Ancient Items. The base requirement for ancient pieces to drop is level 70, and they come with a large increase to the stats that can be rolled on legendary gear (about 20% to 40% depending on the type of stat). Legendaries have a 10% chance to be ancient, and come with a yellow border around its information panel.
This was effectively a form of power creep and allowed players to go to higher Greater Rift clears as well as have a new goal of upgrading all their gear to ancient pieces.
Kanai's Cube Addition and Increased Torment difficulty
Extracting Legendary Powers
Some time after the ancient item change, Season 4 and patch 2.3 dropped featuring a new NPC known as Kanai's Cube.
The core purpose was to allow for players to use newly introduced bounty material rewards to extract legendary powers from items, and equip said powers without actually being on the character itself. Up to three powers (One Weapon, One Armor, One Jewellery) could be equipped this way, and it greatly increased the number of potential builds as well as combinations of legendary items that could be used.
Increased Torment Difficulty
With this addition, the maximum difficulty of the game outside of Greater Rifts was also increased up to Torment 10.
Reforging Rare Items
Kanai's Cube now allows players to upgrade Rare items into Legendary pieces using a large amount of resources, acting as a resource sink as well as a targeted way to obtain a specific gear slot item (similar to Kadala but with a garuanteed chance to obtain a legendary)
Converting Set Items
Third major feature is the ability to convert items from a legendary set into other parts of the same set, using a small amount of resources.
Although the Cube has a ton of other features, you can read up more about it and how to unlock it at https://www.diablowiki.net/Kanai%27s_Cube
Bovine Bardiche and Puzzle Rings can be placed into Kanai's Cube to summon portals for cool places, don't salvage these if you have any laying around!
Season Journey, Set Dungeons, Season Rebirth, and Caldesann's Despair (Patch 2.4)
Seasons received some updates with the addition of the Season Journey, which allowed players to complete specific objectives to obtain season-exclusive rewards. The details are not clear to me (I haven't experienced these myself, I'm a returning player too!) but more or less it gives players a goal in the season runs. Completing specific seasonal journeys also rewards the player with a full starter set pre-determined for their class on that season run, expediting their farming process into higher levels quickly.
You can find season 11 journey map here: https://d3resource.com/journey/
One noteworthy Season Journey reward is the ability to earn Stash Tabs through Season Conquests, one of the only ways to expand stash in Diablo 3. This can only be done up to ten stash tabs maximum, with an additional 2 tabs available by buying the Diablo 3 Necromancer Pack in 2.6
Set Dungeons are a new challenge added that allow players to utilize full specific set to clear a fixed dungeon that has fixed difficulty. There are objectives to be completed in a short time, and players are allowed as many tries as they need to complete it. Completion rewards achievements rather than tangible loot.
Season Rebirth allows players to temporarily remove a character and its items from their roster to create a seasonal character. It effectively allows players with full rosters to participate in a season by "mailing" the deleted character's items to them at the end of the season.
Caldesann's Despair and Increased Difficulty Levels
Patch 2.4.2 added another three difficulty levels, increasing the base difficulty possible up to Torment 13, which is also the current highest difficulty level. A graphic can be found at http://d3resource.com/difficulties/ to view the difficulty values.
Caldesann's Despair is a Kanai's Cube recipe added which allows players to add a large amount of gem stats to a gear as a "Stat Socket". It is a fairly late game objective, and requires various resources and 3 Flawless Royal Gems with the stat type the player wants to add to an item, as well as a highest possible rank legendary gem they can create (Rank 50+) which will affect the amount of stats added. The gem is consumed on use, and cannot be refunded. Caldesann's Despair permanently adds stats to the item and cannot be removed, but can be replaced by utilizing the recipe on the item again. (e.g. Rank 100 Gem = 500 Mainstat)
Primal Ancients and the Armory
Patch 2.5 added another higher quality legendary known as a Primal Ancient. These legendaries have a red border and are essentially Ancient Legendaries with maxed rolls on stats. Legendaries have a 1% chance of being primal ancient. Primal ancients can only be looted after the player has cleared GR70 in SOLO Playon its respective mode (Non-Season, Non-Season Hardcore, Seasonal, Seasonal Hardcore)
The armory was also added, which allows players to save and hotswap between pre-made sets in their inventory or stash quickly, allowing them to change between different gear setups based on their needs. It also comes with smart gem allocation that fills in for empty sockets if the player needs to take out gems for use between different gear sets.
Necromancer Release, Patch 2.6
Not to be confused with Normal "Nephalem" Rifts or Greater Rifts, Challenge Rifts are a snapshot of a player's successful attempt on a Greater Rift that the developers choose for the week, and players will take over their skills, gear and exact setup when entering this mode. The goal is to clear the challenge rift faster than the original player's run using their exact setup.
This mode offers a fun experience for players who wish to try out other builds that may not be a part of the meta, and also offer an easy way to earn quick bounty materials (8 of each cache material and various other loot)
Is it worth buying the Necromancer as a returning player?
Yes and no 🙂
As a returning player from prior to Season 4, there have been enough content patches to change the game drastically and offer a fair amount of gameplay and objectives to clear. I thoroughly enjoyed my new playthrough co-op with friends who have never played Diablo 3 before, especially when trying new classes on fresh characters.
If you have tried every class out before, the Necromancer is a great way to resume your Diablo 3 experience and definitely offers a good amount of play time worth the $15. For veteran players, the 2 stash tabs included are another great reason to purchase it, as a lot of Diablo 3's gameplay revolves around loot hunting and the 2 stash tabs is able to greatly enhance a returning veteran player's experience.
My advice would be to purchase the Necromancer pack if you enjoy the post-story content – I.E. grinding loot, making new builds, killing monsters again and again or pursuing higher Greater Rift clears. With a new class this can easily allow you a few days worth of gameplay.
For those into the leveling experience and/or storyline, the Necromancer pack may not be as great since it does not offer any new storyline. Nevertheless, for $15 you are definitely getting an indie game's worth of your time, and in this case I would weigh my purchase decision against whether I would want to support Blizzard.
General: Legendary Item Changes
With every patch, there is usually a large number of items which become obselete or removed from the game, as well as modified. How your former items are affected varies depending on the item, but Blizzard's take on this is as follows:
Non-Set Legendaries will usually not receive retroactive changes. This means that a meta legendary item in 2.5, despite having the same name, if looted from version 2.1 may have completely different effects and stats.
Set Legendaries may receive retroactive changes, and usually do in most cases. This means that hoarding set legendaries CAN be a good idea, as obselete sets in the existing patch may become powerful in the next patch.
General: Can I still access Darkening of Tristam?
For Blizzard's Diablo Anniversary event in conjunction with Blizzcon last year, Diablo 3 received an event patch which was known as the Darkening of Tristam. The event is over for the year of 2017 and will be back in Jan 2018.
General: Is X gear useful? I played <more than 2 years ago>
Items below level 70 can be salvaged most of the time, as they have no real value besides nostalgia and "exclusivity" to yourself.
All items that are not legendary can also be safely salvaged.
Personally, I would play through the game on a new character, and salvage/cube gear that is not Ancient and is not a set legendary as they will not receive retroactive changes. For instance, Bombardier's Rucksack now comes with +% Sentry Damage in addition to its legendary affix, so it would need to be replaced. I have been informed that certain legacy gear may be good for some builds so I will provide this same advice with warnings!
General: What is the current difficulty objective? What should I be aimming for to be a decent player?
Get to Level 70
Grind gear until able to do Torment 1. Usually a full set of random legendaries is easily capable of doing T1.
Grind gear until able to do Torment 4. Do Greater Rifts for legendary gems to socket and upgrade them as part of your grind
Grind gear until able to do Torment 6. Former highest difficulty.
Grind gear until able to do Torment 13 (GR60) – To reach Torment 13 capable usually requires a synchronized build. If you are not confident of being able to theorycraft strong builds on your own, you can refer to various guides available which spell out item synergies for you!
Grind gear until able to do GR70 (Unlocks Primal Ancients). GR70 usually requires a significant amount of experience and usage of in-trend builds by a new player to achieve in a short period of time, although excessive grinding or strong gear greatly helps.
Current Meta is around GR75 for a casual long-time player, to GR90 for a more obsessed player, and above GR100 are the crazy folks (all respect due!)
General: WHAT STATS DO I ROLL?
Stats are a very class and build specific thing, but the following basic rules and tips should help:
Not all primary stat slots or equipment slots can roll a stat you have in mind. Use Myriam's enchanting feature to find out what stats can roll on a slot. There may be guides out there to educate on this, I can't find one at present so I will link it in future.
A gear that has Single Resist rolls cannot get the All Resist roll on its primaries.
Crit Hit Chance (CHC) and Crit Hit Damage (CHD) is king. Get it whenever available.
Mainstat of your character is usually desirable on all parts
Defensive: Shoulders, Torso, Belt, Legs, Boots
Offensive: Gloves, Weapon, Offhand, Rings, Amulets
Mix/Utility: Helm, Bracers
General: I keep running out of Stash Space. How do I get more Stash Tabs?
Unfortunately, unless you were committed to playing through previous Seasons and their respective Conquest Achievements, there is no way to obtain new Stash Tabs for free beyond that of the gold-purchased 6 Stash Tabs. You can get an additional 2 stash tabs by purchasing the Necromancer Pack, but previous stash tabs earned through seasons (capped at four tabs) are no longer available to you until the next few seasons start.
A total of 12 tabs maximum are currently obtainable by all players. To store gear, you can consider creating empty characters and filling their inventory with obselete or less important gear that you still want to keep but are not currently using.
Seasonal characters also use a Seasonal Stash that is not shared with the non-season characters, which may improve your experience.
General: Where can I find further guides/help?
Visit all the subreddits listed on the sidebar for individual classes, but before making any posts or questions always refer to their sidebar for current build guides. Most of them have updated build links and guides.
For more resources, you can check out:
https://www.diablowiki.net/ – Diablo 3 Wiki
http://www.diablofans.com/ – for a collection of builds from other people
https://www.d3planner.com/ – to map out your build or see statistics
http://d3resource.com/ – collection of useful information and tools from a cool guy
https://www.icy-veins.com/d3/ – large collection of guides, builds and useful resources
https://www.youtube.com/user/Rhykker/videos – Rhykker, build guides and commentary
https://www.youtube.com/user/bigdaddyden76/videos – Anthony Evans, build guides and commentary
https://www.youtube.com/watch?v=U4GyUmNPAuc&list=PLU8etGLqMs3gT46B0sTWSnQ30LGjfE9vX – Daddywarbux, necro guides