It's funny how some here blame Nintendo for reusing engines and assets in NSMB2, when we have game series like Uncharted, God Of War, Assassin's Creed, CoD and on and on doing exactly that. And I don't blame any company for doing that as long as the games are good. It's a tough business and companies have to reduce costs when they can.
We can see a big difference from these series, but still limited for the same hardware.
Try comparing God of War 2 to God of War 3, there is a huge difference because of the raw power difference between PS2 and PS3.
NSMB2 is 6 years after the first one, and for a much powerful handleheld, but it doesn't look much better from the first,
and is easily surpassed by SM3DL when comparing 2D levels.
Considering the raw power of 3DS, we expected something a little closer to Wii version, or maybe even better(beside resolution)
This is why me, and @xwacthmenx are complaining.