My review:
Build quality - Wow...this thing is very nice. It feels like a high end device. Very, very solid.
The Screen--With a 720p 294ppi screen (which puts it right below the Nexus 7 1200p 315 ppi screen), the Shield's screen is very crisp. Colors pop like with a OLED screen.
Performance - 2 GB RAM and the Tegra 4 really shine. The speed is fantastic, like the new Nexus 7. 1080p video runs great. There doesn't seem to be any way of switching between apps like the Nexus 7.
Audio - Goddamn, nice speakers. Quality is really good. My only grip is that changing the volume is a two step process--hit volume button, and then hit the up/down icons in the screen. Weird.
Gaming-I got Dishonored to run with my crappy 6 year old b/g Verizon Fios router, but the game ran smooth with a little hitching (I'm using a GTX 660 2GB card). I haven't tried Onlive yet. I tried some of the new Android Tegra games (Tainted Keep) and they ran very smooth. Where this thing really shines is emulators. N64, Playstation, SNES, Gameboy---this thing is the perfect emulation machine. PPSSPP works, but no controller support until the .9 release, so it's pointless right now.
Ports-OMG a MicroSD card slot! Hear that Google and Apple? A motherfucking, MicroSD slot! The HDMI out works perfectly. I don't know if thing has OTG functions though. I didn't try HDMI out on the streaming PC games function either.