If you like and want something like Diablo 2, which in my opinion is one of the most borderline definitions of an RPG, I'd say give Dungeon Seige and DS2 a try. Both of those games are mindless click-fests like D2 was.
If you want to try your hand out on some real RPG's, try the following:
Neverwinter Nights
Knights of the Old Republic
Fallout 1 and 2
Morrowind (the best RPG ever made, IMO), then Oblivion in that order
Gothic II (fun game, although terrible inventory system)
If you want to try something a little different and enjoy FPS's and RPG's, try the following:
Deus Ex (great game, NOT Invisible War)
System Shock 2 (also a great game)
BioShock (good game, not as good as SS2)
Vampire the Masquerade: Bloodlines (good story, so-so gameplay...worth playing if you can get it for free)
Lastly treading off the RPG path a ways, I would recommend the following series due to its INCREDIBLE atmosphere, if thats what turns you on to RPG's in the first place:
Thief series
Good luck
