Just got to play New Super Mario Bros U at work. I can say without hesitation that it was insanely fun. We played five-player rush mode, where the person holding the pad gets to lay down platforms, stun enemies, and help or hinder the other players. After I got done, I realized how fun this is going to be, giving the pad to my 2 year-old son (who's an iPad junkie), and letting him cause chaos while the rest of my family tries to get through each level. Great stuff.
The pad itself feels really nice. It took me a moment to get used to how big it was; smaller than an iPad, bigger than a Kindle. But it's just another instance of how Nintendo knows controllers. Within moments it felt like the most natural thing in the world. I really liked it.
They were just booting up ZombieU as I left, but I had to get back to work, so I didn't stick around to check it out.