As I have not fully completed the game, I cannot give a legit review. But here are my first impressions on Super Mario Galaxy 2.
Graphics:
Nice, Crisp, graphics, just like the first one. The environments are well detailed, characters and enemies look great, and I'm glad they decided not to change them, and not opt for other styles ["Claytastic/Blocky"]
Story:
Many of you [including myself] will be dissapointed that the story is fundamentally the same as in the original Super Mario Galaxy. Bowser stomps Mushroom Kingdom flat [literally], captures the princess, and heads for the center of the Universe. But seriously, who buys Mario games for story? Leave that to Legend of Zelda.
Gameplay:
Brilliant. It doesn't seem QUITE as unique and original as the first one, but it takes everythinthing you loved from SMG, multiplied it 10 times, and threw some fresh stuff in too. So far, it's great, but there are a few inperfections. (Yoshi controls are a little wonky, extra lives are too common)
Audio:
Excellent music, combining spooky, techno, and even jazzy songs, every single one catchy and well done, make the right mood for the right levels. It's so good, I wouldn't mind having a couple of the tunes on my iPod.