Nobody ever mentions the Gothic series... OK, the third one was a bitch to play with all the bugs, and the first and second have unconventional controls, but the atmosphere, storyline and characters beat everything else I can think of.
If you can't handle decade-old control systems and graphics, try Risen. It's pretty much the same, just looks better, easier to control, and unfortunately has a completely different world than the Gothic series (copyright reasons, but same developer team)
Also, when it comes to RPGs, Fallout 1, 2 and New Vegas can't be ignored. The third one was a bit empty and boring for my taste, and never played Tactics and the console shit Brotherhood of Steel.