Coming from an IndustryGamers article...

Some people have been holding out hope that Nintendo is going to unveil the final version of the Wii U and it's going to blow everyone away with its graphics capabilities. That scenario, however, is looking more and more unlikely all the time. While multiple developers are on record saying that the Wii U's hardware is in a state of flux, unofficial sources continue to place its power comparable to the Xbox 360/PS3, not above them.

I honestly wouldn't mind if the Wii U was just a bit more powerful than 360/PS3. We haven't seen a single Nintendo title with beefed-up graphics since the days of the GameCube. I'd love to see what Nintendo could do with visuals from the 360/PS3 generation.