The screen? Amazing. It really is beautiful. It makes it VERY difficult to go back to using my N7 as my primary couch/living room tablet. The screen on the N7 is fine, but having such a high resolution at a 10" size just makes browsing the web and playing some games so much more enjoyable.
I admittedly haven't had hours upon hours to play with it, but 4.2 does seem pretty stable on it. I haven't had any Chrome Browser crashes, but even if 4.2 isn't stable or Chrome has issues on 4.2, they will obviously be updated shortly to update that.
Performance has seemed great. My friend played a couple hours of Angry Birds in Space or something, and it looked incredible on the screen and played flawlessly.
After she was done, I pulled out a micro-HDMI cable I have for my ultrabook and plugged it into her TV. The display mirroring was flawless (in 1080p resolution). I played some trailers from the IMDB app and some movies from the Play store. The quality does appear to degrade just slightly as I saw some macroblocking on the 32" LCD TV, but none on the N10's screen. Also, performance does slow down slightly when the display is mirroring. Meaning, scrolling through menus and stuff appears to have a slightly slower framerate, although it never really stuttered completely or froze.
Speakers are excellent. And the build quality, while plastic, feels great. It feels thinner than the N7 in my hands, and feels very light for a 10" tablet. The ergonomics of the tablet make it pleasing to hold. I still feel the 7" form factor is easier for "couch browsing", especially with one hand, but I can't imagine many 10" tablets feeling better ergonomically than this one.
Haven't had a chance to test out the cameras or video playback of different files yet, but I can confirm that photosphere is available on the N10 rear camera. I believe you can fit probably 2-3 movies from the Play Store comfortably on the 16GB version (which I have) before storage starts to become a concern.
In short, it really is the device most of us were expecting it to be.