Grim Dawn is the most fun I've had with an ARPG in years. The class system is very interesting and, as far as I know, unique to this game. Rather than just being a barbarian or necromancer or whatever other typical ARPG class you can think of, your class is determined by selecting any 2 archetypes. For instance, maybe you like being a pet class like necromancer, but you want to have a slightly more active play style than just watching your skellingtons paint the map red. So, you mix in the Nightblade (melee rogue) class at level 10. Your new, combined class is called a Reaper, and you have access to both skill trees, free to mix and match as you wish. Very interesting playstyles can emerge from creative pairings.

I am a casual player so I can't offer any perspective on the endgame or anything like that, but if you're looking for something to scratch the Diablo 2 itch with a fun twist on classes,you cant go wrong with Grim Dawn.