I can't see how this fills a void in the set top market. It isn't a console. It isn't a pc. It isn't solely a video device like a roku. This is basically the same thing as me plugging my tablet into my TV. Or chromecasting my tablet through my roku. Or plugging an hdmi cord into my pc.
I disagree, I have had a shield portable, the tablet, and now the TV. Especially after the updates and the move to lollipop, there is nothing out on the market that touches this. Yes, Android TV needs a bit more TLC, but what is there now is a seamless, extraordinarily slick experience you can't get from other consoles. It makes the Roku look pale in comparison, and if you're using game-stream, it makes all consoles look lackluster as well.
At this point (not at the beginning) it's a super refined experience and Nvidia will continue to update it. I am lucky enough to have a computer with a Nvidia card (the initial reason I got the portable) , and it's crazy-fantastic for that purpose. I stream games from the Grid as well, sometimes even preferring the grid games over the ones on my rig as I can pick them up and go while on the road.
I never understood the whole OUYA thing, but I am starting to see it in the shield - there are some good android games out there, but NVIDIA has gotten some good controller support on a solid selection of android games which are a great addition to PC games as they're a bit more casual pick up and play things than you find on Steam.
So right now, I hit the game pad button, get voice recognition to the point that it blows everything else away, and can generally navigate to what I want a lot more intuitively than a PS4, tablet or XBone. And it's just rock solid - no jitters, no stuttering (okay, on a bad day a grid game does stutter a bit, but you'll quickly forget you're playing from the cloud and the graphics beat the snot out of PS4 and XBone).
The HomeRun benefit is actually quite good, as I'll be using it as a cable box in another part of the house when they upgrade for MPEG2 support.
So I see the shield TV as a great swiss army knife, something that I use everyday quite regularly, and I know that I haven't seen half of the neat stuff they have hidden underneath there.
Is it completely different than a Roku? Not really, but it is a helluva lot better. Think of it as a Roku 8 - the shield skipped 4-7 and set the bar higher. While I sound like a fanboy, I got into the shield as I couldn't run any solid HDMI signals in my house due to super long cat6 runs with some interference. The shield fixed all of that, and it essentially has allowed me to transport my 70 pound rig to any 1080p TV I want.
I can't comment on its 4k abilities as I don't have a 4k TV, but I wouldn't underestimate this device, I don't think any other set top box can touch this thing.