It has MMORPG vibes, particularly with the gathering/crafting systems and little side quests, but it doesn't have an "endless endgame" to speak of. It was my first thought, too—if OP isn't looking for an endless endgame loop, then Amalur is a great suggestion.

Lots of Diablo clones have endless endgame and single player, but not sure if they'd be what OP is looking for. Last Epoch is the best of them all, imho. I saw Grim Dawn recommended; it's also great. Torchlight 2 has a WoW-like cartoony aesthetic and is pretty great. Titan Quest is the other obvious req in this genre, and there are many, many Diablo 2 mods that add new systems and end game loops. (Path of Exile 1 & 2 are both great, of course, but they're online only.)