superchunk on 05 January 2013
The Dolphin emulator is very good otherwise they'd look a lot more different.
Even with that the Wii U version has better textures, backgrounds, and a lot of various improvements to things like water/liquid effects, certain enemies, lighting, etc.
Obviously there is a lot of shared resources that had little to no upgrades with the exception of better resolutions. Doesn't really matter as both games are fantastic and well worth the $$. (especially considering I got my copy of NSMBU for free)
