The handheld feels pretty good. It's nice and comfortable, with a rubber back to it. The d pad feels like it's halfway between the NGPC's pad and the one from the Neo CD pad, I like it better than either. The face buttons are pretty good as well. The L and R buttons at the top aren't that great, but they are only used for switching aspect ration (L buttons) and pausing (R buttons.)
The screen is pretty good, although not as good as the current lineup of handhelds like the Vita or 3DS. I'd say it's about on par with a PSP 1000's screen, maybe a hair better.
After playing with it for two days, I'm really happy with the handheld itself. I do eagerly await someone figuring out how to hack a Unibios in it though, so I can turn on red blood in the appropriate games.
I'm super happy with the stick, especially since it works with the PS3 and PC without a hitch.
The only thing that's really disappointed me with the thing is the quality of the AV out.