The truth is right now there isn't. The 3rd party support is not as high as it was with the Wii and the developer tools out for the Wii U are underhanded right now. I would buy a Wii U in like 3-4 years when there's a price cut with actual games you would want to play.
The 360 and or PS3 have established libraries, the 360 having great online media services. If you like the games on another platform more than the Wii U, I suggest you return it and get something you really want.
I learned my lesson to never keep a console hoping some good games would come down the line. The Wii had like 3-4 games I was ever interested in and it wasn't worth the $550 I paid during launch.
3rd party support not as strong as Wii? On a two week old console? BWAHAHAHA. Also, dev tools underhanded? What do you mean by that? Nintendo provided dishonest dev tools to devs? Considering what has been done with the likes of Madden with contracted a contracted dev cycle on an infant platform with a novel control method, I think not. Not quite optimized, yes. Somehow dishonest or unnecessarily difficult to dev for, I doubt it.
360 and PS3 are on the verge of being replaced, the investment into those libraries, if previous entrants haven't been enough to lure your purchase, is unwarranted. I say give the Wii U a chance. Get NSMBU and any other of the 30 launch titles interest you (NSMBU is a must have, though). ACIII is great on the platform, Madden (while missing the infinity engine) is great and makes amazing use of the gamepad. Arkham City is another title that makes great use of the GamePad.
The 360 does have great media features, but nothing that isn't available as well on Wii U (netflix, hulu, amazon instant video, and wiiTV forthcoming) other than Microsoft exclusive properties (as far as online media is concerned, there isn't much, and xbox music, xbox video, and many xbox live enabled games are also available on Windows8)
All in all, make your own choice as to what to do with it, but there is definitely some exciting potential there, and some great launch titles that should keep you busy. Xbox360 is an asesome platform as well, and in my opinion you would be very happy with that as well, but as I said before, it is to be replaced soon. I would keep the Wii U and wait until the next Xbox is released to enter that ecosystem.