I'm currently in the process of playing the game, not trying to 100% it as I have massive trouble reaching some Star Coins (there is a star coin over in 1-4, the final one, which in hindsight is so simple to reach yet it alluded me for about two or three hours). From what I can say as of now, NSMB2 looks like the same-old same-old, but it definitely does not feel like the same-old same-old. Whereas the easier side of the Mario spectrum (for example, Super Mario World, NSMBDS, NSMBWii) were easy throughout regardless of what the aim of the playthrough was, and where the harder side of the Mario spectrum (e.g Super Mario Bros 3) were hard all around, NSMB2 takes the two and meshes them together.
Getting to and jumping on that flagpole is perhaps the easiest thing to do in the game. Now, I'm not the most astute critical thinker out there, but I can say that several Star Coins will give even the most veteran of players some trouble. Whether it is reaching what is in plain sight or finding what is unseen, there are several very cleverly hidden Coins and of course the Secret Exits don't make themselves all too obvious either.
Coin Rush, while I haven't gotten through too much, is great in concept but in practice I feel a "score runner" mode would benefit the mode so much more; what any Coin Rusher plays for is coin count, not score count. While both are so similar the differences are pretty much insignificant, I find that being able to play for either would make for an infinitely more engrossing mode. That's just me.
My sole complaint about the game thus far, like legitimate complaint, is that co-op mode is only for local play. Nintendo can do better, I know they can. I guess I SHOULD be grateful that a coop mode even exists, but I desire for more.
As of now, NSMB2 gets an 8/10. But, I'll judge when I vanquish World 6.