1) Borrowing from another game DOESN'T MAKE THE GRAPHICS LOOK CRAPPY.
2) If you can't tell the difference between the DS and Wii game (because you seem to think that almost everything was borrowed from the DS game, even though that isn't close to the case), I don't think you're judging it correctly.
The game does not look crappy because it borrowed textures and models from other games.
It looks crappy because it does not use the graphical power of 3DS the way it should.
Let's make a little comparisson.
NSMB DS
NSMB2
SM3DL (2D levels)
SM3DL shows an outstanding 2D for a 3D Mario,
it has good 3D effect and excellent graphics.
Seeing what SM3L done, I expected something a little bit better for NSMB2,
maybe it could look closer to the Wii version.
The graphics are really bad, but there are many things that make this game even worse.
It's not even in 3D. Games like Muttant Mudds and Mighty Switch Force proved that it's possible to have good 3D effects on a 2D platformer.
The boss of middle's castle is always Reznor, turning the game very repetitive.
There aren't any new power ups, just a variation of fire-flower
There aren't any of the power ups of Wii version.
There is no Yoshi or Baby Yoshi.
The bosses except for bowser are all variations of Bowser Jr.
There aren't any new music.
The secret paths are too predictable(ghost houses and castles)
With all that said, I can say it's the worst Mario platformer I ever played,
I trully regret buying this, and do not recommend it for anyone.