might contain spoilers
I already got 40 stars, what really is amazing is the levels and how creative they are, in each galaxy you have 6 levels and always 2 of them are special levels where you can only get 1 star (like that waterway where he is surfing over a flooting waterstream.) each normal level has 3 stars and almost always (or always) you can 'buy' (with those stars you can collect with pointing your wii-mote) an aditional way to get a star (an new little planet or somehing else crazy) and there are also special stars where you have to finish the level in a very fast time or enemy's move faster so it's harder.
the amount off end-bosses is really a great thing , in each galaxy you got a real end-boss (such as bowser or that mechanical thing you see in the movie's) but almost in each of the normal levels you have to fight to other level bosses (like the baby piranaplant), they are al extremely fun (but not really hard).
the graphics are really good, water is beautifull (nintendo always makes it beautifull), the characters are awesome, bowser and some of the end-bosses look really good. and flags look absolutly stunning too (yes they really deserve to be mentioned).
Controls is where the game really shines, everthing just feels so great, the spin attack, collecting those little coloured stars, throwing stuff, and the power-ups (bee mario feels far better then I would have ever anticipated).
story is not really special but still better then in sunshine, what I like is the why you collect stars, afcours to save peach, but to do that you need to power up your base of operations and it's just really good done.
The music in this game is just phenomenal, o lot of old songs return (remix and original) and a lot of cool new ones too, almost all orchestrated.
overall it's just gaming awesomeness
oh and for the people who are afraid it's too easy, it can be a really difficult at times, not really becouse of enemy's though, it's the levels who will sometimes make it hard for you. With those special stars though even enemy's can be very hard and the real chalange in the game is to get all of these.
