A shared open world, end game dungeons, and a new take on gear and skills
An open world experience
Diablo IV will be introducing a shared open world, which is a first for the franchise. Social hubs will allow players to engage in actions similar to an MMO, such as trade and party forming. Players will be able to form Clans, as well as utilize ingame voice and text chat. Local coop will also be available to console players.
As for the open world aspect, world bosses and other events will appear for players to hop in and join. Dungeons will start as a private event, where only you and your party will be interacting with it. After completing a dungeon or story event, non-party players will be able to see and interact with each other in the Overworld. Furthermore, there will be open world PvP for those to engage in as well.
There will be some players who will not want to engage in these social additions to the game. Lucky for them, none of these features are actually require to participate in. Solo players will still have plenty of options to enjoy Diablo IV with a more solitary experience.
Dungeons and the end game
It seems that Diablo IV aims to make the end game experience more dynamic and varied. The most important gameplay aspect of the Diablo franchise has always been its dungeon crawling. In Diablo 3, increasing the difficulty would also increase your chance for better loot. Diablo IV plans to expand on this, while also creating more variety in the end game content.
Along the way, enemies will drop a Dungeon Key for one of the hundreds of dungeons in the game. Using a Dungeon Key will turn the corresponding dungeon into an end game version. Each key will have a listed difficulty and an affix that will affect the dungeon. During the demonstration, one key made it so that a pillar of lightning would slowly chase the player throughout the dungeon. It was unkillable, and would continuously do damage to player once it was in range.
Along with these changes, dungeons are getting some nice quality of life improvements. They will still be randomly generated, but will no longer require loading between floors and zones. Events that happen in previous zones will also affect connecting zones as well, leading to a more seamless exploration.
In addition, random events can now occur in any location. In Diablo 3, certain random events would only occur in certain locations. Diablo IV plans to do away with this in hopes of creating a more varied experience.
Build variety and gear/skill synergy
Most of the meta builds in Diablo 3 revolved around Gear Sets. In Diablo IV, the focus is to make Legendary gear on par, or even stronger than Gear Sets. For Lengendary and Gear Set pieces, they will come in regular and Ancient versions. The final tier of gear is Mythic, which will have 4 Legendary affixes on it. Only one Mythic item can be equipped at a time. With the introduction of mounts, players will be able to customize them with their own gear and traits as well.
Skills have been overhauled as well. Leveling up will grant skill points that can unlock new skills, or ranking up existing ones. Each character will also have their own Talent Tree, giving players more choices in playstyle variety. Since Skills will now have ranks, one possible affix gear can have is a point in a specific skill, further increasing variety in build potential.
As of writing this, their are 3 classes: the Sorceress, the Barbarian, and the Druid. Each class looks like they will offer their own unique feel to combat in Diablo IV.
Diablo IV is being developed simultaneously for PC and Console.