Of all the games I have played it's close between Dragon Age and The Elder Scrolls 4 Oblivion. In Dragon Age it's much easier to make a visually appealing character, but Oblivion I feel is just a touch deeper.
I hear that APB is Unbeatable in it's costumization, but I haven't played it so I can't judge yet.
I hear that APB is Unbeatable in it's costumization, but I haven't played it so I can't judge yet.