Got to play one today. Controller does feel nice, it's not heavy and it is very comfortable.
NSMB - I enjoyed it and it nice to see Mario in HD but nothing ground breaking unless you count being able to cling to blocks. It looks pretty decent on the smaller screen too but the multiplayer mode is useless.
ZombiU - Some interesting ideas but there's not much going on. It seems like there's always some screen effect going on that distracts you from the fact it doesn't look very good. Controls are fine, the live inventory and the scanning function are nice uses of the second screen for a launch game.
AssCreed3 - Seemed to have some serious frame rate troubles at times, otherwise indistinguishable from the PS3/360 versions. The current/wind dispay on the second screen is a decent attempt but doesn't really add anything.
Rayman - Was probably the most fun I had with any of the Wii U games, but I don't see how it would be interesting single player. Most of the game pad stuff was gimmicky but at least they were trying something different. Also used the "pro controller" for this and I know everyone has said but the the buttons under the analogue stick is beyond stupid.
Sonic Racing - Ran at about 20fps for some reason, looked decidedly worse than the other HD versions. The second screen was a map with some 1/4 screen videos if something happened. Apparently it supports full play off the gamepad but it wasn't available
Batman - is Batman
Darksiders 2 - is Darksiders 2
Nintendo Land - lol
Came away with no real change in interest for the machine, if I didn't have a 360 or PS3 already I'd be more impressed by it. Nothing you didn't already know.