i like this game, no point about that. its just not as good as it should be.
as you could read in the gamespot review, there are 3 types o f levels:
speed, shooting and treasure hunting. so there is no problem with the variaty. a bigger problem is tough, that the shooting levels are no fun at all. its just holding the b-button, lock-on some enemies, and fire away. speed and hunting is just better.
storyline is a bit lame. i mean, how many videogame heroes have some knid of dark version of themself? there is mario/wario, link/dark link, and sure to be more. besides, sonic allready had one: metal sonic!
and at last, twoplayer is not much fun as well. you can fight each other, but you can't as well. if you keep homing in on each other, you just stay at one point and get nowhere. but if it sucks this bad, why do i like it? because of the speed levels! these are just plain fun. bashing through all of the enemies is as good as it feels. and although its not good, you just like to play it!
majura's shopping advice: if you see it in the bargainbin, just buy it!