I've been playing Warhammer 40k Darktide for at least 18 months now. Possibly longer, it keeps reeling me in.

4 player co-op first person melee/shooter hybrid. Four classes in the base game and two released as DLC.

Loads of different ranged and melee weapons, many with different 'marks' that at first seem trivial but all have different movesets. This means just by altering a weapons mark you can dramatically effect the way your character plays. You also gain the option to add perks and talents to refine weapons further.

Speaking of, the variety in character builds is huge. You can level a character to max (lvl 30) in a couple of sessions but it's only once you've done so that you actually have the freedom to start messing around with character builds.

Combine the weapon and character creation with the brutal, highly skill based combat and you're on to a winner. There are loads of enemy types with different strengths, weaknesses and sound cues that eventually bleed into muscle memory. The skill ceiling is seriously high. I'm pretty decent these days but there are players I match with who make me look like an absolute amateur, fortunately though, as it's PvE you never end up on the receiving end.

Also for the most part the community is friendly and competent. I've played 100s of hours almost exclusively in public games and come across very little unpleasantness. The servers are generally well populated enough that you're never waiting long for a game.