* hack-and-slash sort of game
* no monthly fee
* you can do all content (on all difficulties) either solo or in co-op mode, with a party of up to 5 people
* monsters HP/damage scale depending on number of people in the game
* mob spawns occasionally have extra abilities, this can go from a group of champions (3-5 elite-like monsters) with e.g. fire damage to a single 'named' mob with minions (e.g. closer to wow boss with adds all at once) that all do knockback or have thorns,...
* bosses can be stunned and sometimes even knocked back because you're simply THAT powerful
* random dungeon layout and mob spawns means every game is different.
* side-dungeons have some extra quest/loot but are not linked to main story line. Often only one of 2-3 of these bonus dungeons can be found within a single game
* item stats are more random, e.g. even a unique that has a guaranteed Strength bonus can have any value in a range of say 200-250.
* item sets have unique bonuses and often look great together
* only some items are class-restricted, but most cross-class items still look different on another char (e.g. sorcerer looks like he's wearing robe while same armor piece on a barbarian may look more like a plate chest)
* when solo playing, you can have a mercenary helping you (templar/tank, scoundrel/rogue or enchantress/mage in D3), they do low damage but are often valuable for slowing effects or just meat shielding, they also have 5 tiers of abilities, always choice between 2 abilities per tier (so even your merc has a talent build!).
* mercs can also equip some items (jewelry & weapons + a special merc-only relic slot)
* healing is done throw health globes that can drop from monster kills (or hitting a boss) and heal everyone
* all abilities have runes (glyph-like stuff) to enhance them
* There are only a limited amount of skill slots available, switching skills cost time (more akin to the WoW MoP talents, but then all active abilities you can have are in there.
* loot drops are personal, only when YOU drop something, it goes into the 'world floor'
* no soulbound items, you can sell what you have used
* AH allow people to use RL cash to buy items and even gold (with a cut to Blizzard ofc)
Think that's most of what I can think of in 3 min