We've known for some time that the Wii U version of Super Smash Bros. would be different from the 3DS version, but Nintendo's been pretty quiet about what changes we'll see. Thankfully, Amazon's spilled at least some of the beans. Looks like we're getting a stage creator utilizing the GamePad, Master and Crazy Hand challenges, and a board game mode.
According to GameSpot, Nintendo has specified that the GameCube controller adapter will only work with Smash:
"The GameCube Controller Adapter for Wii U is compatible with Wii U and Super Smash Bros. for Wii U specifically - it is not compatible with any other Wii U software. The adapter is also not compatible with Wii and we apologise for any confusion."