I also recommend FlareRPG [0] to try out. It has way more pleasant navigation than Diablos, reminds me a bit of the Divine Divinity [1], which is also awesome single-player game.
It's an entirely different game (more of a CRPG than action), but the more modern Divinity Original Sin games are excellent too. DOS2 is my favorite RPG, and it can be played by itself (its story has basically no links to DOS1)