Comparing it to other high profile games its really not on the charts, but comparing it to the prior recent sonic games, or half the crap shovelware nonsense the Wii is flooded with its an alright time waster. That's really what it is, the game you either rent and blitz through in the afternoon and never see it again, or the thing you buy blitz through in the afternoon and play on the odd occasion because your Wii is sitting there gathering dust and you feel sorry for it being so underused.
I've played past the proper end, and it's still unlocking new things to do in the levels, but its all becoming a bit "collect x" "kill x" "don't get hit" and beat the level on each of them.
It's most certainly not the best game out there, and once you've played it all once, it holds little replay other than to get a higher score and some higher ranking stars, but really it's a one go through "oh its done" put it away forever type game. I liked the story from a nostalgic point of view, not a normal games good plot point of view...
So yeah, rent it and play it, have some fun and never think about it again, or buy it, just so you can say you have a bit of me history before I made it big (shh, it'll happen eventually)