I chuckled, but I agree with what I think is your sentiment.
Level design is hugely important. I agree with you there. But mechanics matter greatly. The mechanics inform the level design.
I'm not just talking about new tools like suits, Yoshi, FLUDD, or even gravity, but I'm even talking about handling and physics. Additionally, new movesets like triple jumping, long jumping, backflipping, etc. informs the level design. All that stuff goes into making Mario games stand out from each other, and NSMB changes none of it. How about adding some new moves that could really let us reach new Mario platforming heights?
NSMB looks to have less creativity in its four games than between SMB and SMB2 or SMB and SMB3 or between SMB3 and SMW. I'm especially disappointed because I thought maybe the coins would make for some interesting gameplay situations, but they really add nothing gameplay-wise to the game. Hell, anyone with a 3DS could tell you that Donkey Kong '94 added more to the Mario formula and moveset than the NSMB games.
Sure, level design matters, but you have to be damn creative if you're not going to add any of the other tools, moves, and gimmicks to Mario's bag of tricks.
So in regards to my Van Gogh comment, honestly, if the whole game presented new gameplay mechanics such as the type I listed, it could keep its sterile, lifeless presentation and horrible music and it'd probably be GOTY material. But it doesn't add those mechanics. And the artstyle perfectly epitomizes the resistance to change in this series.