Summary: Upgrade NSMBW to HD? Check. Include fantastic level design? Check. Justify the purchase of a Wii U? Not really... as it's a LOT like NSMBW. However -- it's still incredible. The addition of the Miiverse interaction is very nicely done, and doesn't intrude into the gameplay so much as it makes it better (plus it can be turned off if you don't like it). This game made me want to go back and run through NSMBW again.
Summary: -Story/Length- Your story is your same old, same old Mario. Princess is taken, Mario must save her. Though this plot has been used so many times now, its not getting old as it is turning into a staple of Mario games. Thus when it is changed people go crazy over it. The games still sell though, and why? because of the tried and true plots of these games still offer polish, the same workable plot, and offer a bunch of content for completionists.
Summary: Awesome game. Had to reorder due to mine getting misplaced. Definite buy for the Wii U along with Super Luigi U. I recommend this for anyone who enjoyed mario's adventures on the nes and snes.