If Mario 3D world is one of the worst 3D Mario's, then New U is one of the worst 2D Mario's. The gameplay is sloppy, but more importantly the levels and many of the boss fights are just poorly designed. I haven't played 2D Mario since the SNES and was looking forward to this game. It's a shame this is what Mario has become.
I've played this game like 3+ times and it's still a fucking mediocre ass 2D platformer, despite being probably Mario's best 2D platformer purely form a level design perspective, it's only real competition being Super Mario World. Play just about any other 2D platformer you can get, and if you really want a multiplayer 2D platformer so badly, just play Rayman Origins or Legends. Both are leagues above anything the NSMB series has produced.
Got this game bundled with my Wii U, it might not be very original but it was all I needed at the time. Really enjoyed the new stuff such as the Baby Yoshi's and the new music, and New Super Luigi U was more of a fresh take on the series as a bonus. Enjoyed beating both, but I'll admit there is not that much to be said about these games.
This game does almost nothing new from any of the other New Super Mario Bros games, but it is still fun to play. It does not have as much nostalgia for me as the Wii version, but I still feel like I got a good amount out of it. There a few creative levels that stand out such as the painted boo level that make one wish that the whole game had that level of creativity. The main reason the rating is as high as it is is because of the Luigi mode. Making everything a timed mode and having a jump that is deceptively tricky make sthe game a lot more fun for someone looking for a challenge. I never liked that in 4-player mode someone had to be Nabbit, but looking back I realize that every time I managed to get 3 other people to play at least 1 of them probably needed to be Nabbit