The amount of overhype this game is getting is ridiculous! Here are my impressions after the 5th World:
Super Mario Galaxy 2 is fun, but shallow. The game keeps introducing new ideas, and doesn't do much to expand on them. Now, these are great ideas, but they come off as cheap because the levels are extremely short, and they are pulled together by these puzzles and ideas. Most of the time, I complete the stint expecting more to be done with the idea, but the level ends, and I end up thinking "That's it?"
An example of this is having to clear and create a path for a Chomp to follow so you can get it to drop in a hole. It's a very basic path, but the idea is really cool, and you expect that after this "tutorial" stint of the level, you'll start the real meat of the level that expands on this idea. That never happens, and the level just ends. Then another level comes in, introduces a cool new idea, but that idea never gets expanded on before the level ends. And that idea is soon forgotten to introduce a new idea.
The drill powerup is the exception, and it's too bad that the levels are so short. I wish all the drill levels were rolled up into one massive level! Great idea, and I can say that it's been used very well so far.
But so far, Super Mario Galaxy 2 just feels like really shallow, forgettable fun. While I admit that the first Galaxy isn't my favorite game, I found it much more meaty and complete than this game at this point in the adventure. Galaxy 2 is high in quantity; there really are a lot of creative ideas going on, but since they are rarely expanded upon passed a very basic level, I can't say that it's high quality. It certainly is not a 10/10 game for me.
NOTE: I don't hate this SMG2, and I'm not saying it's bad. But it gets enough praise as it is, and I just don't agree that it's a perfect game.