Mario is a good game to get, if you like the 2-D stuff. A lot of replay value with this one. Trine 2 is a good pick up The Cave is also good. It kind of reminds me of Maniac Mansion. There's demo if you want to try first. Scribblenauts is good buy.
There are more, but these are the games I keep going back and playing on my Wii U.
Currently playing: Resident Evil 5, NSMBU (4 star Profile) NNID // XBL: Dynheart
I bought the bundle today at GameStop. They only had one in stock. I didn't have a lot of time to mess around with it before I had to leave for work, but I enjoyed the bit of ZombiU that I played. Now I just have to wait for Monster Hunter. After sinking so much time into Tri on the Wii, the graphics in the demo were very pretty indeed.