I have 30 stars so far and it's a great, great game. However, I am not completely satisfied with it and as rami said, it's not as amazing as some people make it seem to be, at least not in my opinion. Well, it might be a bit unfair to say this because I can't think of many platformers which I have enjoyed more. It's just... I dunno, it has been really entertaining but hasn't completely amazed me I suppose.
The level design is really fantastic. The levels have a lot of variety and are insanely fun but I do think all of them, even the largest ones, are too small. There's little to no exploration because all the star quests so far have been very linear. I really miss larger levels, I loved wandering and finding cool stuff in Mario 64 but in Galaxy, it's like playing a sidescroller in 3D, you know? It's cool in a way since the are no boring moments whatsoever and it's a lot of fun all the time but I can't help but miss exploration and large, open-ended levels. Not that Mario 64's levels were that huge but definitely larger than Galaxy's.
Another thing which bothers me is how damn easy this game is. I'm not let down by this since I was expecting Galaxy to be this easy but damn. Why can't they make a difficult platformer for once. If Mario was actually challenging, it could be so much more entertaining. It's too bad really. Also, I have only played a few hours and already got 30 stars so Galaxy is pretty short which is a shame.
Actually, those are my only gripes with Galaxy. Camera system is fantastic, gameplay is almost flawless, it's got some amazing level design, a lot of variety and minigames, excellent music... it's all-around a great platformer and definitely one of the best games I have bought this year. I don't know if I like it more than Mario 64 though, and I still prefer Twilight Princess to Mario Galaxy (fite for best wii title..) but who knows, that might change. But that's no reason to not get this game. It's worth your money.
... And exploring the castle was so much more fun than exploring the observatory.
