My main complaints of Sonic Shuffle would be:
-It needed more mini games, and it needed a better way to activate mini games (You needed to land on "event" spaces, and even then you might not get a mini game.). I'm pretty sure I played a game where, aside from accidents, not a single mini game occured. That can make for a pretty weak party game, with all due respect. I'd expect more mini games in a newer version or sequel.
-Loading times. I've played some games with bad loading times before, but this one took the cake. When added together, they extended a game with my friends by at least 15 minutes on average. I assume it wouldn't be as much of an issue in a newer rendition, however.
-Flawless computer intelligence. Sure, they made a few mistakes here and there mini game-wise, but if you had a movement card they wanted/needed, they'd take it, with no guesswork involved; it killed most of the single-player fun in the process. Such intelligence would be easy to nerf in a revision, of course.
-The monster battles. They were responsible for >=50% of the game's loading times, and they were ultra-lame to boot (Choose a card, then be virtually guaranteed to win or lose the "battle" depending on your choice.). If they do anything with this game, they'd better do something about this. If nothing else, they could make it, I don't know, a BATTLE?
Despite its obvious flaws, it was still a decent game. Playing it with actual players compared to computer players made it a great deal more enjoyable, as well.