You non-haters (lol) gotta understand.
The Mario games up until NSMB were all extremely well-crafted labours of love, and that's a big part of why we love them so much. They ooze soul because dozens of crafty japanese enthusiasts poured their soul into it, for hours and hours.
That's clearly not the case here, and to a lot of us, it feels straight up sacrilegious. When Disney started making low-budget straight-to-video sequels to the Jungle Book and other classics, that felt wrong too. Where there's a tradition for going all the way, a cheap cop-out is heartbreaking.
Even if a big portion of the NSMB audience is okay with the same visual style, I think Nintendo is making a mistake here. The new Mario audience will grow up to love Mario even more if it has more of that special "je ne sais quoi" that comes from serious artistry. Kids accept whatever is fun, but they can feel the difference between something deep and something shallow, even if they appreciate both in the moment. As a child I was in awe of Super Mario World, and it developed into a fondness that made me a fan to this day. I spent hours on other decent (but generic) platformers in my youth too, but I've forgotten many of them. The feeling of something thorough stays with you, and grows.
Do you guys really think a brand new Mario with all the bells and whistles & freshness that SMB3, SMW and YI had (when they first came out) would sell less than a new NSMB game? I don't think so. They could easily make the game play exactly like the other NSMB games, just with richer visuals and audio. But the best thing would be to actually respect the legacy of Mario by making something brand spanking new without sacrificing what already works.
It would be a far better way for Nintendo to cultivate their brand too, instead of this fast food version.