I wouldn't really call what Mass Effect provides a Role Playing experience. It's at best a failed attempt at one. Every action that your character takes, and the way he is, is determined far more by the predetermined elements of the game than your own personal input. I fail to see how pushing a character through a limited number of paths creates a real sense of actually having a significant amount of control over him, but then again I'm not so easily pleased by interactive storyline gimmicks that are really all Bioware have to offer.
FFXIII will be the far superior game simply because it relies on storyline immersion, a practise that actually works, in delivering a role playing experience (as well as the far more talented developers working on the game).