Allright, a few hours in, and here's what I'd like to share:
-No extensive loading times. At all. And I'm a very, very impatient ************.
-No controller problems, though I've only played with two so far. The Wii U GamePad felt unwieldy as hell, the Classic Controller Pro felt amazing. In either case, I haven't experienced the C-stick momentum problems people have brought up.
-As of the first day, online is absolutely outstanding. I've got a strong connection, and input lag is very minimal, pretty much like it is for offline play.
-Audio does break slightly at the beginning of certain menu screens or (very rarely) some matches. Presumably unnoticeable, but I have my volume jacked up.
-Very minor: Framerate is erratic while playing around with the camera angles in in-game pauses.
-I'm rather peeved at how I can't fiddle with the control configurations of controllers without having to associate it with a name. I was hoping that the Wii U version would adopt user-oriented preferences as defaults like the 3DS version has.