Thoughts on balance:
1. There should be fewer attacks that can't be dodged. We've got, what, lightning, Pow, blue shell? (I think all those can be avoided if you have a star, but not if you've got something simple like a banana peel. Which is about what you can expect if you're doing well enough.)
2. Items that fuck the guy in first place but don't actually help the person who uses them need to go. Lightning's not going to help you if you're in 12th place.
3. If they're going to weight items to what place you're in, there should be weight for what course you're on too. Oh, I'm in 12th place on Rainbow Road and I just got a gold mushroom. Thanks, game, I can totally use that if I want to fall off the edge again.
Rubberbanding is a topic all its own, and all in all I feel like the single-player is less a game of skill and more a game of luck and rote memorization. Which would be all right, I suppose, if I could unlock shit while doing online multiplayer. (Uh, I can't, can I?)