Which game should i get?

Well i have an xbox 360, and i'm really content with it. just not sure which game to get. if you could list your favorite xbox/ xbox 360 games below. I'm not looking to spend too much on this, so like couple year old used games is what i'm searching for. Oh, and after you put your favorite games, tell me this. i love roll playing games (Fallout, Elder Scrolls, Borderlands ect.) and i was thinking of getting a new one(s). Whats your opinion on the Mass Effect and Fable series? They're popular, but are they worth getting? If so, should i start with the first ones, and make my way up, or would it be ok to start with the latest? Thanks again. the game