Well, all that rumor and speculation came true after all. Nintendo unveiled the successor to the Wii console at E3, and it is called the Wii U. It is pronounced like "Wii You," since Nintendo says it is a perfect fit for the individual user, U, while still carrying the gaming-together theme of the Wii. If you want a lot of details on the Wii U, you'll have to wait since Nintendo didn't disclose a real lot at its E3 press conference, but there are some facts on it. First up, the Wii U is about the same size as the Wii, but it is capable of outputing 1080p graphics over HDMI. That's right, the Wii U is a high definition game console from Nintendo at long last. The game discs will be the same size as a DVD and be a proprietary format, similar to the current Wii discs. The Wii U will be backwards compatible with Wii discs, the Wii Nunchuk and Remote, and you can download and play games on it thanks to some internal Flash storage. The storage can be expanded with an SD card or through the USB port, like with a USB hard drive. No word on just how much storage it has internally, but early reports seem to suggest it'll be 8GB.
The controller itself incorporates a 6.2" touchscreen, which brings a new level of interactivity to the console games. There is a stylus that slides out of the controller to use with the touchscreen, which makes you think it could be of the resistive variety. Nintendo did show off some fairly complex sketching with it, so it seems to be a pretty capable touchscreen in its own right. It isn't a high definition screen, but Nintendo did say its a larger resolution than the 3DS screens and is comparable to a modern-day smartphone. There are two circle pads, similar to the one on the 3DS, on either side of the screen. The left side has a directional pad while the right has A, B, X, and Y buttons. There are two shoulder buttons up top, two trigger buttons on the bottom, and the Home, Start, and Select buttons below the screen. It also packs motion controls similar to the Wii Motion Plus, though due to its size, you won't be waving it around like a Wii Remote. There is a front-facing camera on the controller, a headphone jack, and built-in speakers so it seems Nintendo definitely wants you to use it for video chats.
The controller can play games on it without having anything display on the TV (if the developer allows), but the portability of it only exists within range of the Wii U console since the Wii U streams video to the controller. You can use Wii Remotes and Nunchuks with it, with players using the Remotes having split-screen gameplay on a TV while the person using the Wii U controller will use the built-in screen. The Wii U controller appeared to have a different camera angle and even different controls than the Wii Remote players, with it looking like the person using the Wii U controller was pitted against the people using Wii Remotes.
Finally, the 1080p graphics. Nintendo kept quiet on just what was powering the Wii U, but games did have dynamic lighting and shadows, light shafts, high dynamic range rendering, full reflections, bump mapping, and antialiasing. So it appears the graphic capabilities are pretty high, but it is unclear if the console was upscaling to 1080p or actually displaying games at 1080p. Either way, Nintendo does have an HD console for the HD era at long last. The controller does have its own GPU and gets its content streamed from the console, but the graphics on the controller seem just as capable as the console itself.
I am sure there will be plenty more features on the games for the Wii U, but for now, this should give you an idea of what to expect from it. The Wii U is expected sometime in 2012, though Nintendo did not say when for sure.