besides some challenge that's a bit harder than i would have liked, this is a very good game for your mario collection.
EQUATION TIME :P good game+ new ideas that are still good=VERY GOOD GAME :D
that's pretty much what this game is. they took the good formula of super mario galaxy 1, and added new ideas to super mario galaxy 2. a good example is that yoshi, like mario, was given new abilities. like the ability to run on water, to shine light in dark places, and to float. these are new and original, but they don't hurt the feel of the mario series. why? because mario galaxy put innovation into the different challenges this game presents.
But with putting so many new ideas into a game, you have to use those ideas in a meaningful way. i'm not saying these were bad ideas, but these added some difficulty i felt could have been avoided. for example, i had TERRIBLE luck with the purple coin missions. i understand time limits, but time limits in video games are the bane of my existence. i can't STAND time limits. otherwise, this is a very good game, one of the best in the mario series. this is why you won in the 16 bit wars. you managed to keep going on a successful streak, instead of making PINBALL GAMES! :P (no offense to sonic fans by the way. i'm a big sonic fan :D)
Check out my channel, i plan to do this game as an LP eventually!