You have to hunt down the adapter, too, which can be a bitch.
Or, you can get
THIS. It connects to a Wiimote. I have two of them for SSB and they work great, and it's exactly like a GC controller. If you don't already have a Wiimote, you should get at least one for backwards compatible games that you may want to play, all Wii games are backwards compatible with the WiiU, and if you want to pick up, say Xenosaga, or the AWESOME Metroid Prime trilogy (just released recently on the eShop), you'll want a wiimote and nunchuck. Plus, if you already had a Wii, you can transfer over all the games you bought through the Wii eShop and use this GC controller instead of the "classic controller" which I HATED the design of.[DOUBLEPOST=1424606255,1424605881][/DOUBLEPOST]
The Pro controller is so much more pleasant than using the big controller-pad for anything that can use it. Bayonetta 2, Hyrule Warriors, both better with the pro controller IMO.
Though for Kart, have a wii-mote and nunchuck. I just find that the most pleasant for whatever reason, even more so than a "regular" controller.
I actually prefer using the gamepad for most games, I like having the maps and such at a glance instead of having to pause the game and pull one up. For games that don't really utilize the screen on the gamepad at all, though, the pro controller is usually better.
I'd love to see them do a remaster of Okami using the gamepad. Using the celestial brush was SOOOOO much easier on Okamiden for the DS because you just drew it on the lower screen, and if you translated that for the WiiU, it would be fantastic. I mean the Wii port worked well with the wiimote better than the PS version, but using the gamepad would be even better.