I'm not sure why it hasn't been brought up yet, but a pictionary like game would be PERFECT for the Wii U. Game and Wario's version is great, but it only feels like the start of a great idea
A game I'd love to see is Mario Casino. Anybody remember the mini games in New Super Mario Bros and Super Mario 64 DS? Well there were a bunch of card games where Luigi was the dealer. My sister and I would play with each other all the time. Can you imagine being able to do this with the two GamePads that the Wii U can handle? It would be phenominal! Imagine the online capabilities as well as single and local multiplayer!
I also really want a Wii U version of Pokémon Stadium/Battle Revolution for Gen VI. Always loved those types of games.
There's so many ideas possible for the GamePad and it's disappointing we don't really know what is ahead for the system