I got a Wii U a few days ago, played a bit of Nintendo Land and Mario Bros. U... I like it. I'm a Nintendo fan so it's a bit biased. Still, I'm not impressed. The gamepad feels cheap, I would've preferred actual trigger L and R buttons.
While Miiverse is cool, the best part about it is admiring people's drawings. The rest is just people writing "cool game," "hard boss," etc.
The Gamepad honestly does seem like a gimmick to me. Aside from some interesting uses in Nintendo Land, it's been annoying. Often the TV just tells me to look down and use the gamepad, meaning my TV is just sitting there doing nothing. Other times it's just wasting battery because it's just working as a second TV screen.
Finally, the obvious one is that Nintendo is releasing this hardware so late. We all know that. But whatever, I'm really excited for Pikmin 3!! :D