I'm sort of glad that pre-release GAF shit on this game so hard for being a rehash and lowered my expectations. Now that I'm playing it, I'm really having a lot of fun with it because I didn't expect too much.
In the past, Nintendo probably would have just ported the Wii version, like they did with other console-to-handheld stuff. At least the levels are new, and the game actually looks pretty nice. As good as I remember the Wii version looking and though the 3D is subtle, it sometimes looks kind of cool (especially in lava stages).
Yes, it's true that 2D Mario usually has different artstyles and music and this one doesn't. However, a lot of the graphic differences back in the day were due to technology advances and apparently Nintendo has Mario how they want the games to look. Shame about the music, still.
Remember DKC 1-3 on the SNES all had the same artstyle and they came out pretty rapid fire and people loved it. Sonic 1, 2, 3, Sonic & Knuckes, and Sonic CD all looked pretty similar too, and people loved it. NSMB came out in 2006, NSMB Wii in 2009, and now NSMB 2 in 2012. It's really not as milked as it could be when you really think about it.