Graphical limitations. Difficulty of porting to the motion controller. Lack of sufficient buttons to move, shoot, sprint, open the power menu, order squadmates around, reload, switch weapons. Content not safe for whole family (language, violence, illicit substance references, etc). Unable to contain the awesome of having Adam Baldwin voicing a character.
not just graphical but content wise you would have to use about 10 wii disk just for part of the story