NSMBU is an excellent game, and if you can't tell the visual difference between it and NSMBWii you are blind. Or playing both on a SD television or playing Wii on Dolphin. NSMBU is in high def so the difference is dramatic. Beyond the resolution increase, the graphics are signifcantly better, with more visually impressive worlds, cool lighting effects and so on.
That said, the style is similar. Nintendo went with NSMB as the big Wii U launch title because the series is insanely popular and it is also cheep and easy to make. This gave them a full extra year to work on more complicated big titles such as Mario U, X, MarioKart and Retro's game. But personally I think they could have done much more to make it a better title and a true landmark title. The NSMB series has lost a lot of its impact. Mario3 or World were high-end, massive titles. NSMB for DS was landmark in its own way, bringing back 2D gaming and dramatically updating the series visuals with polygons. NSMBWii added 4-player, which was a huge, fun addition. NSMBU adds HD and some cool new level themes, but still feels a bit like the Japanese SMB2, which as Nintendo said at the time, really didn't differentiate itself from the original enough.
NSMBU should have added much more in terms of content, visuals and gameplay. It should have been longer. Add some more worlds. It should have more varied themes with some really crazy levels. It should have some more really different levels with puzzles or other tricks. The visual style should be majorly updated. The game could learn a lot from 2-D games like LBP or Trine2 and really push visual boundaries even though its in 2D. And with some simple additions fans would be excited: Add 3 or 4 more unique powerups. Make Peach playable. Easy to do.
I think Nintendo is scared to push boundaries on its bread and butter classic title.











