Apparently more powerful then the PS3 by a bit. But due to the new nature of the console, dev's have not yet found a way to unlock that power efficiently, while the well trodden path of the Xbox and PS3 provide dev's with solutions to unlock the most potential out of the console.
As it stands at the moment the specs from a technical standpoint the Wii U is the highest. But from a realistic standpoint, the Wii U is only mildly more powerful then an Xbox, and the PS3 is more powerful then the Wii U.
By the time the potential of the console is unlocking, the Wii U will be more powerful then the ps3 but Xbox will most likely be close to releasing their new gen console. Why Nintendo why? You could of made a stunning machine, but you chose an underpowered console yet again.
The same thing will happen again, people will buy the Wii U for the gimmick, just like people bought the wii, kinect and move, and it will barely been used, except by diehard nintendo fans who must play the exclusives, although Nintendo have gone back to the more serious gamer roots as well as the casual market, the wii has given Nintendo a sort of stigma of a casual gaming device and customers and dev's will most likely treat it as such initially, until decent evidence suggests otherwise.
I'm surprised by the lack of Bluray as well, it doesn't bother me as such, but could be a selling point to others.
Now I have gone through my negative points of the system, I will go to my pro points,
It looks like a decent system, I think the controller is a brilliant idea in fact. The main problem I have with console games and PC ports is the HUD console games require. Often a menu and HUD have to be built to accommodative being far from the screen and sitting on a sofa, simplifying descriptions and making a menu that is very awkward to traverse, but best you can do with a controller. The Wii did make this better to some extent by using the wii-mote in an almost mouse like way... this did strain your wrists though! The screen on the wii-U is a brilliant idea, and it may be a very good solution to menu's in games that require good inventory management ext.
They also seem to be supporting indie devs in the console store which is great! Although I haven't much into this, only heard bits hear and there. I know the Xbox is awful for indie dev's to update their games as they only get the first patch/update for free, from then on to update their games it can cost them I think 10 grand.... not good for customers if there is a bug that needs fixing and a company cannot afford that fee.
But yes overall I think the Wii U is a decent console, but in my opinion it should of been made slightly more powerful to stand even a remote chance with the eventual next gen consoles. Once they come out I feel as if they will just sweep the Wii U under the rug, shame to be honest, Nintendo is probably the least tyrannous of the three console companies. The price seems right though, and if I had a decent source of income I may very well think about purchasing one eventually, once I hear more game related news from it.
Thus concludes my rather ranty reply, I may be wrong all of this was news I remember from the top of my head!
You are the Nintendo fan so feel free to correct me if some info is lacking.