Havok
Super Freak
I'm a FPS freak, but I've heard so many good things about this game. The only rpg I've played a little of was SW KOTOR. I thought it was pretty cool.
KOTOR was my first real RPG that I played also. Fallout 3 is a great game, very wide open and so much to do like others have already said. Just don't go into it expecting a hardcore FPS just cause it has guns and a First-Person Perspective, it still plays very much like an RPG.