"Shield Pose" tasks you with pointing the WiiPad like a shield, either to the center, left, right, or above, to block darts being shot at you by pirates in a fleet of ships. This is done to the rhythm, so you get musical cues about when to point which direction. "Left, right, over!" and then a beat, and then you move to the left, right, and top of the screen in the same cadence. When you correctly point the shield, the darts appear on screen as if they stuck to the virtual "shield," and then you must shake downward to remove them. And that functionality, the darts on the virtual shield, is literally the only thing about it that couldn't be done with a Wiimote.
At the end of the demo, I was asked to "dance" -- shake the pad to build up power for the fireball attack I had for some reason -- and fire it back at the pirates.
But that's not the important part. What's the thing feel like? In an artificially extended word, awwwwkwaaaaard. It's designed so that the players holds sort of the top area of the controller, and my (admittedly small) hands were placed such that my thumbs fell naturally onto the analog sticks. But not the buttons. Though the Shield Pose demo didn't require buttons, I tried it, and I had to make a very conscious effort to actually hit the face buttons instead of unconsciously tapping the circle pads while I was going to do something.
The demo also didn't make use of the touchscreen, so I can't speak of its quality or ease of use at the moment. Other demos did use this feature, and I will get hands on as soon as the opportunity arises, along with more detailed impressions of the rest of the functions. I will say that while the display on the touchscreen looked really similar in quality to the Shield Pose demo, it didn't appear to be HD itself -- and the Shield Pose game was extremely graphically simple, in the style of first-party "Wii" series games.
I also played the New Super Mario Bros. Mii demo, but I was one of the Wiimote-based players, which meant that the experience for me was "Oh, hey, New Super Mario Bros. Wii."