Ok, so after what feels like A LIFETIME OF MARIO STAGES, I've finished every last damn level in NSMB2 with exits & coins.
And...it's still meh.  I feel like that guy who said Tekken has too much content.  There are just so many freaking stages in NSMB2, yet 95% of them are boring unimaginative filler.  There's a couple of creative stages (mostly the A/B hidden levels), but not a single one of the 50+ stages reaches the high of some of the better 3DLand or Galaxy stages.  It definitely feels like a fanmade Mario game.  It goes through the motions but brings nothing to the table.  I didn't hate it, and it was moderately entertaining, but at the end of it all now it just feels like wasted time that could have been spent playing a better game.  Hope the Wii U game is more interesting.