I remember seeing a comparison video between Batman Arkham City or Asylum for Wii U and Xbox 360 and the Wii U was inferior, suffering from frame rate issues. That said, there are certain ports such as Rayman Legends that utilize the gamepad in such a way as to be unique and arguably superior to the other versions.
If you're looking for the latest, greatest next gen experience than Wii U is not it, but it's still cool and unique in it's own right. I like those old, rehashed Mario games, though I believe the next Nintendo NX system would benefit from more powerful hardware. Unfortunately, I heard a recent rumor that the Nintendo NX would be less powerful than PS4. I don't know if that's true, but it's a bummer if it is.