I'm one of those people who vastly prefer 3d land to 3d world for the same reasons, so I understand you.For a certain demographic, I suppose. I never really played 2D Mario for the multiplayer experience. And while 4 player simultaneous co-op is a neat novelty, it's still tethered to everything else that many have raised issues with. Plus it arguably compromises the level design of the single-player to some degree.
And by that point, Kirby's Return to Dreamland would have already introduced many to 4 player co-op the year before, lessening the impact. Of course, it's possibly it was itself inspired by NSMBW...
But you said "irrespective of what one may think of the quality of the games themselves" which makes what you or me think about the game quality irrelevant, the game did push boundaries and that what I meant, and didn't Kirby's Return to Dreamland released 2 years after NSMB Wii?