The Wii U tablet is just another controller with some neat applications.
Nintendo guides most of our attention to the Wii U touchscreen controller. There are some neat things you can do with the tablet controller in single player mode and in multi-player. In multi-player mode the gamer holding the tablet has a different view of the game than the others who use the Wii controllers. Nintendo shows this concept in the Mii Chase demo. The tablet offers the ability to implement new gaming concepts, but I think this is not enough for a next generation Nintendo home console.
The Wii U hardware specifications are kept vague. Nintendo said it will be 1080p HD and run on an IBM Power-based multi-core CPU. Playing Nintendo exclusive games finally in HD will already sell the Wii U to many Nintendo fans. I have though the feeling that Nintendo has one more major thing about the Wii U in the back hand that will actually make it a worthy successor to the Wii.
It could be a surprisingly low price, better than PS3 performance or yet another gaming experience (Kinect?). The reception of the Wii U is mixed this week at the E3, but Nintendo actually needs a new blockbuster console.