IDK you guys but I enjoyed a lot New Super Mario Bros
The problem isn't if the New Super Mario Bros games were good or not, they were excellent platformers in fact, especially the Wii one.
What we don't want is another Mario title using almost exactly the same style and mechanics.
We already have 2, well arguably 3 games with 3D land, that uses very similar designs, just look at the difference between Mario 3 and Mario World, both games share the same universe but are very different in terms of gameplay mechanics, music and visuals.
It wasn't just a game with improved graphics and a set of new levels like when comparing NSMB to NSMBW, it was a whole new experience rather than just another sequel.
While I don't usually complain about sequels to good games I would much rather have something fresh, even more so given the new processing power as Hadrian mentioned.
Personally I never liked the style of the New series that much, I would've preferred a style akin to Wario Land on the Wii or Mario Galaxy but in 2D.
What I do loved about those games were the physics, the very accurate controls made the games perfect for speed runs and stuff like that.