so mine got delivered yesterday and had a quick play....
first off it was set at 4k in the display settings and my A/V amp does not appear to like it! artifacts and display flassjhing off and on through the tv. so i plugged directly into the tv (which is 4k) and all was well.
apps and games are limited but if you install sideloader for app shortcuts and use the es file explorer then you can load APk files from usb. have installed google drive which opens everything i have on there, documents, videos etc.. installed dolphin browser but cannot navigate anything, may need to try a keyboard for this? Modbro works perfect, showbox loads but again, can not navigate the layout.
controller seems okay, d-pad is a bit squeaky! can talk into it for google and appears to work on PC if you plug the usb into it, bonus!
so my rig is a bit tame currently, a pentium k and 770gtx so as expected, streaming games was choppy...so i went to my friends house to test streaming.
very good results, wireless and wired using virgin 50mb. test rig was i7 4790k with 980gtx, monitor was 4k super wide LG which may have created the next problem.. resolution on tv when steam/game streaming! so it all looked a bit stretched/zoomed and the choices were 1440 and when we changed the ratio it made no difference?
that said, GTAV was very smooth at 4k adn tried Grid 2 and no lag there either. ultimately the gamestream is mirroring the monitor so if your PC is close enough, you might as well get a longer display cable.
menu browsing on the shield tv itself is rapid, loading 4k via youtube is reallly quick, opening files and loading apps is nice.
you can run games like asphalt 8 and those generic shooters and they look ok but not a patch on what it can display but for the kids, it saves draining the battery on your tablet or phone.
no facebook login or web browser out of the box, its all google login stuff which is not too restricting so far.
sorry for the waffle but if you want me to try anything with it then i am more than happy to give it a go for you and give feedback!