Jeff used the dreaded b-word talking about NSMB2 on the Bombcast. I've been playing it for a week or so now (got a review code awhile ago). I normally see eye-to-eye with Jeff on games, but I disagree here. Sure, it's a retread and it's basically just 'more new super mario bros.' but that said, the quality is there and I'd totally recommend it to 3DS owners. I'm an older gamer and am sadly finding fewer and fewer games holding my attention - especially handheld titles. But I'll happily play NSMB2 into the ground. I'm a Mario fan (I played 22 hours of 3D Land, I think) and Mario-wise, there's no dip in quality here. It's solid.
Wondering whether Jeff just whizzed through, or if he went after the 3 gold medallions on each level? I think it makes a big difference. Revisiting levels to grab Gold medallions you missed the first time through makes you experience levels differently, and showcases the game's search and discovery elements, and seeing levels twice instead of once sheds light on how well-designed Mario games always are. How big gaps are, koopa placement, everything in exactly the right spot to maximize fun.
TL;DR it's a different (and much better) game if you task yourself with getting all the medallions, and far from boring.
Edit: yes, the b-word is 'boring.'