Everyone has listed the exclusives already so I won't do that. Instead, I'll just say if the trailers and gameplay of those exclusives look interesting, then you won't be disappointed. If none of those exclusives interest you, then it won't be worth your purchase, obviously. I have had an absolute blast with my Wii U already and I think the best games are yet to come.
I also didn't realize how awesome having BC with the Wii library and GBA and DS virtual console would be. And Earthbound. :) I skipped the Wii generation so catching up on Metroid Prime Trilogy, Xenoblade Chronicles, Pandora's Tower, The Last Story, Skyward Sword, etc. has made the purchase even more worth it for me.
But even so, I would actually wait until E3. I think we'll see a price cut by the holidays and maybe some incredible bundles. You've waited this long, right?
It'll be awhile before I figure out how to do one of these. :P