I'm at World 3 right now. The game is very good. The soundtrack may be extremely similar to NSMB, but there's a lot more variation in the songs depending on what world you're in which is really cool. Can't forget the little bongo tracks that get added in when you hop on Yoshi, too.
Mario's movement is more polished than NSMB; however, with the soft Wiimote D-Pad (instead of the DS' "clicky-ness") it takes some getting used to. After you get used to it (read: takes about one level, if that), it's just fine. Lots of little bits and pieces from all Mario games gameplay element/soundtrack/sound effect-wise which is very nice.
Oh, and if you're wondering if the Spin Jump being mapped to shaking the Wiimote is awkward... it's really not. It's just a simple upwards (or downwards) movement that feels about the same as jumping in the cow racing mini-game in Wii Play. It's just right. Just be careful if you're knee is shaking or you're moving around a bit or whatever because it can be very sensitive. Overall, it's good. Also, you can use the Spin Jump to put a little challenge on yourself (instead of using a jump to clear something) or throw some style in there, if you like.
So, to end all the "lol its a nsmb port. stupid." talk: It's very good... it's worth it... you'll definitely enjoy it when you get it.
EDIT: (World 3 map music is really good. I like it.)