I see a lot of MMOs being recommended, but I find them to be either shallow in combat or predatory unless you are seeking MMO specific things, so I’m going to point at single player/coop stuff.
Bethesda has a large selection of open world games, but I pretty much assume people have played all of them (Elder Scrolls / Fallout games).
If you are okay with going outside of Fantasy, the Far Cry series has some impressive technology in their older titles. Far Cry 2 is a personal favorite, your PC might be able to handle it.
Borderlands series.
The original Dragons Dogma: Dark Arisen holds up. This is probably my best recommendation based on your asks.
Lego Star Wars or the Lego Marvel game.
Fable 1, 2, 3
The Middle Earth Shadow of Mordor / Shadow of War Games were pretty incredible but might be too high-end.
The first Red Dead Redemption might run for you.
Early Dark souls games might run. Maybe 1 or 2.
From here, I would start listing old Star Wars Jedi Knight series games.
I could probably go on, but this is most of the good stuff off the top of my head.
I forgot to add Mass Effect. Great for sci-fi, great leveling, and combat.