#diablo4 sorceress is designed to be fragile -- expected 🤷♂️
#diablo4 barbarian looks very mobile, can equip 2 2 handed weapons and 2 1h weapons-- can get more Legendaries equipped than any other class.
#diablo4 druid when you use your werebear/werewolf skills you instantly transform and back as needed for the skill you're using, no need to maintain a form unless you're doing it to keep up certain passive bonuses.
Skill point tomes can be found to increase progress on skill trees. Bottom of trees are strongest talents, and you have to choose between your options (can't have them all).
#dianlo4 Open world stuff: shared and contiguous world. Dungeons continue to be private between you and 3 other members of your party.
Campaign overworld areas start as party private but after completing your objectives you will see other players.
#diablo4 max party size right now is 4 including you.
#diablo4 open world is shared with other non party players in sort of higher numbers and it varies by area. Most of the open world is meant to feel a little more isolated and dangerous, but towns and world bosses show many more players.
You can play with others regardless of your progress in story.
You'll have access to party voice chat for whatever you do, including pvp.
#diablo4 supports 2 player couch co op on consoles. Split screen baby~
All best content etc will be available to players regardless of if they prefer solo or group play
#diablo4 has clans and clan bank systems.
#diablo4 dungeons: foundational part of series and critical part of legacy. Lots of dungeons! Dark and dangerous.
#diablo4 Dungeons are randomly generated.
#diablo4 also has randomly generated "dungeons" outside.
#diablo4 no more loading screens switching between dungeon floors!
#diablo4 tilesets blend seemlesslt together-ruins to caves to who knows what. Lots of variation and random generation.
#diablo4 has random events in dungeons and overworld. No longer restricted to certain overworld areas like d3.
#diablo4 dungeons have dungeon objectives. Objective progress increases rewards and danger in dungeons. More enemies might start coming after you and these can happen in boss fights.
#diablo4 endgame dungeons: keys drop that work on specific dungeons, have affixes which can affect players, environment, mobs. Have ranks that are harder. 
Any dungeon can become endgame content by finding its key.
You can salvage dungeon keys for crafting if you don't want to play it
#diablo4 has "families" of monster types connected by fantasy. Their functions compliment each other and all have varied abilities and mechanics.
Skeletal ballistae can shoot characters from off screen. Inspired from how players could be hit offscreen in d2.
#diablo4 elites return. New affixes called enhancing affixes which take monsters base ability and enhance. Different for every monster. Applying the multiplication affix to fallen shaman let him multi resurrect minions, on ballistae it increases shots.
#Diablo4 every class has a short evade ability bound to space bar that lets you get out of dropped aoe abilities, avoid incoming abilities. Classes have unique abilities to break out of stuns and strike back.
Bosses in #diablo4 can be staggered by building up stagger meter with stuns, freezes, etc. When bar is maxed, each boss has unique behavior players can do that radically change fight (breaking off arms, other stuff).
#diablo4 adds ancient sets, ancient legendaries, and mythic quality in addition to usual gear qualities
+skill points form gear allow players to break through skill level caps like in d2
Regular Legendaries and set items are developed to be roughly equal in power and usefulness. Not locked into sets.
#diablo4 mythic items are most powerful. Limit is one per char.
Runes and runewords are a thing. Condition and effect runes. No more hidden runewords, you build them yourself. #diablo4
Some runes. System is still in iteration and sounds like some progression system might be in works for rune quality perhaps
#diablo4 is a base and expansion selling model. No selling power for microtransactions.
#diablo4 builds can be customized with gear, skill choices, ranks of abilities unlock new components of the same skill. Skill points aren't just power increase.
#diablo4 will not have an offline mode but you can do everything solo.
#diablo4 trading - loot from mobs is priority but there will be trading. 3 types of tradables, some can be traded freely, some can be traded just once and become bound (you can wear before trading too), some will be bind on pickup.
Tradability of gear is still in flux and they encourage fans to discuss it online
#diablo4 pvp - with all gear and skill combinations, they will fine stuff as problems arise.
#diablo4 Legendaries will be a bit more rare than in d3, but harder content will obviously reward better gear. It sounds like magic find might not be a thing this time, you just have to do the harder content. Unsure on this.
#diablo4 gear affixes will be random within a range. Plan to support modifying affixes but unsure how yet.
#diablo4 post game support - will have seasons, goal is to change up experience for each. No specific plans yet. New legendary items each time. Will likely be many other things that will change each season. More in future.
#diablo4 will have a hardcore mode.
