Some games I would recommend that are either RPGs or have RPG elements:
Deus Ex: Human Revolution
-- Great story, great atmosphere, great gameplay, with a few minor flaws and bugs. Can be had for rather cheap now on the 360, I think, although the PC version is superior.
-- The first one is a modern classic. Again, great story, great atmosphere, great gameplay. Get it.
Legend of Grimrock
-- This is a roguelike in the mold of the old Eye of the Beholder
type games, but with modern graphics. Very thin on story, but lots of fun and varied gameplay.
Duke Nukem Forever
-- Like the others, great atmosphere, great story, great ga... hahahaha, just kidding! Not as terrible as its reputation would have you believe, but probably not worth your time.
Fallout 3/New Vegas
-- If you didn't like Oblivion
, you may not like this, unless you are more comfortable with post-apocalyptic settings. But really, the gameplay style is very much in the Elder Scrolls mold (given that it's made by the same company.)
-- An action RPG/FPS hybrid, but with a cool atmosphere and Diablo-like loot drops. It's fun. There's also a sequel.
series -- If you liked the Diablo games, you would probably like this.
series -- Ditto.
I'll let you know if I think of any more. Many of these are PC games, but I believe most are also available on the 360.