There really haven't been more than a handful of decent RPG games for the 360. I played Fallout 3 on the PC, and wasn't impressed compared to Fallout 1, 2 and Tactics. Fable 1 & 2 were both quite good games. KOTOR 1 & 2 are of course great games. If you enjoy games such as GTA, I'd say give Saints Row 1 & 2 a shot. People discount these games just as GTA clones, but they are actually a lot of fun to play. SR2 gave more options in terms of character creation, but both games are very good. You can modify all vehicles (aside from planes and helicopters, of course) and there is a decent weapon selection. You can get help from fellow gang members to assault other hideouts in the game (provided you get a car with more than 2 seats, otherwise they will steal another car and follow you), and it is an open-world environment that doesn't leave areas of the game locked until you get so far. You can access all areas of the game from the start, and there are some really good minigames such as insurance fraud that help to kill time (insurance fraud is a ragdoll game that has you throw yourself into traffic to rack up a high enough settlement claim... it can waste a lot of time with a good amount of laughs if you are doing it right).
People say Dragon Age is great, but I got bored of it rather fast and just got my way through the game in under forty hours just to finish it off. I couldn't get drawn in by the story, and the characters didn't really keep me interested in the game. But that's just me. You might try browsing around on XBL to see if there are any decent indie games on there that spark your interest as they are usually cheaper than box titles. Actually, I think I might do that myself soon. Still waiting for my brother to beat Red Dead Redemption already so I can go rent something else.