Werehog. They almost got Sonic back in greatness, believe it or not. The Sonic levels are fun, addicting, and best of all, fast. They control fluidly and, although they don't have near enough challenge to them, can be played over and over and still be fun. The best parts of these levels are when they switch to the sideways view.
On the other hand, the werehog levels have a stupidly deficient combat system, tedious and punishing platforming elements, and overall repetitive level design. The werehog itself literally caused this 8.5-9 game to drop to abyssmal levels. Plus there are far more werehog parts then Sonic parts.
Then the story became all ****ed up because they made it too childish. (HUGE understatement here.)
GOTY Contestants this year: Dead Space 2, Dark Souls, Tales of Graces f. Everything else can suck it.
