My local Target has the console, but none of the demos are playable yet, so, basically, all you get to do is scroll through demo videos read about a few of the games. The videos I watched had horrible jaggies, but most games generally do when you play them at the supermarket(I remember Halo Wars was practically unplayable on their TVs), so I'm going to assume that was Target's fault for setting the console up poorly.
There were no demos, but I did get a hold of the the (batteryless) controller. It didn't at all feel like holding a tablet. The curves on the back of the controller fit the shape of my hands perfectly, and the balance felt just right. Definitely more comfortable to hold than any Gaming handheld. My only complaint in this area is that holding it one-handed feels very awkward. The controller is very light(it barely feels any heavier that a wired 360 controller), but with the added weight of the battery, I'm not sure how my weak wrists will be able to hold up. Fortunately, I doubt many games will force you to use the controller one-handed for extended periods of time.
The button placement felt pretty natural to me. My fingers were easily able to transition from the face buttons to the joystick and back again. I especially liked the joysticks. I've always found the sticks on the Xbox 360 to be a bit too tall for my hands, but the Wii U's felt just right. The triggers felt good too, but the Z buttons were a bit awkward for me.(as most L/R buttons do). Overall, I do like it more the the Wii's classic controller plus, and a LOT more than Sony's Dual shock(which I've always despised). The 360 controller still reigns supreme in my eyes, but I can see myself playing games with the Wii U-pad, even if they don't use the screen meaningfully.
The aspect that I found the most impressive, probably because of the disparaging way I look at resistive tech, has to be the screen. , It actually seemed to be just as sensitive as the Vita's capacitive touchcreen, If it weren't for that stylus, I'd actually have trouble believing that it's resistive at all, as it recognized even the gentlest of touches flawlessly. The viewing angles were pretty good as well, and the colors seemed to be fairly accurate from what I could tell.
Overall, it seems pretty solid. It's always fun handling new technology, and I'm actually pretty excited to try out some actual games if/when the demos become available on this unit, or if my Bestbuy finally gets the console.