Grim Dawn -- if you're into Diablo or Path of Exile like ARPG's
It's hands-down one of the best games I've ever played. What makes it so unique is how in-depth the builds and play styles can be. Endless combinations and replayability.
It's an "M x N" combinatorial thing.
There's something like ~10 classes, with 3 "skill trees" each.
You can (and should) choose a second class after first few levels.
Now you've got (10 ^ 2) class combinations, with 3 skill trees for each that you can freely use.
Then there's a whole thing with types of damage (fire, poison, lightning, etc) and you can tailor builds around this, with both skills and equipment bonuses.
On top of it all, it's moddable. So people have released mods to add Diablo classes into it, plus the classes from another game by the same publisher (Titan Quest).
Can play solo, or co-op (LAN or online)
I can't do the game justice with a single text comment tbh. Just have to try it, if it's your kind of game.
https://store.steampowered.com/app/219990/Grim_Dawn/
Buy the entire set though if you really want to experience it, not just the base game.