I realize there's a dedicated X10 thread, but this is obviously a busier corner and the unit is proprietary, so the only people interested in a review would be 850/900/A/B owners. If someone wants to cut and paste this into the X10 discussion, I'll be glad to stick my head in and answer any questions.
I have the Sony 55x900A: aside from normal issues with tweaking settings (and bum HDMI cables), I've been very satisfied with the picture. My expectation with the X10 was to be able to have a hub that could facilitate rental of 4K movies and perhaps the odd demo clip. Because my ISP is capped at a glacial 15mbps download speed, I had no expectations about streaming 4K via Netflix. I was wrong, but more on that in a moment.
You can find information on what hardware is included with the unit elsewhere: I had little issue getting it up and running, save for Sony's insanely annoying Entertainment Network credit card entry. I had to try several cards before one was accepted. Something to do with having to have the address exactly as it appears on your CC statement, caps or nine-digit zip included. Whatever.
The X10 really just gives you four content options: running your own 4K material (I don't), selecting from your pre-arranged 4K Library (stuff you've downloaded/purchased/accessed), Netflix, or 4K Video Unlimited, the Sony storefront for movies and a little television.
I first went to 4k Video Unlimited and selected a few nature clips, 4-5 minutes in length. These were free and came pre-loaded on the X10, since they were available immediately without needing to be downloaded. (Despite being $0, I still needed a SEN account to "buy" them.) The only free clip I selected that needed downloading was the trailer for Spider-Man 2.
Next, I looked at their library of 4K titles. There is simply no way I'm paying $29.99 to own one, and not all are available to rent, so I settled on Monuments Men because A). it's a newer film (and thus should look cleaner in 4K) and B). I haven't seen it yet. Regarding my slow-motion ISP, I took note that the film was averaging about 1% for every 4-5 minutes. That means about 8-10 hours to download the two-hour feature. (It's also worth noting that the X10, owing either to its internal policies or my ISP, will not download two things at a time: it "paused" Monuments Men so I could d/l the Spider-Man 2 trailer.)
The Short Clips: Underwater stuff, bee stuff, butterfly stuff--all the standard nature segments typically seen playing in a loop at retail. Everything looked fine. Clear, sharp, but nothing dramatically different from a torched HDTV playing 1080p in a showroom. I sit about 9 feet away. Squatting closer (4-5 feet), there was no degradation in quality. It was all very pretty, but nothing that made my jaw drop.
Spider-Man 2 Trailer: Again, pretty. Colors popped nicely. As a completely subjective observation, I'd say the vibrant blues and reds of Spidey's costume seemed 20% more "popped" than 1080p.
I then went to Netflix and decided to see if 4K would even appear as an option. (Note: this was after MM had finished downloading.) I had been told by a Netflix phone rep, in a very scoffing and dismissive tone, that I shouldn't even think about 4K content unless I had a 50mbps connection.
To my surprise, not only was House of Cards listed under a 4K content banner, so were several films I didn't realize had been added to the service: Smurfs 2, Ghostbusters, Philadelphia, Hitch, a nature program, and a couple of other options. I hit the nature selection expecting it to buffer like crazy or turn into a fuzzy mess in the same way 1080p content will get chopped in half on me due to a busy or bad connection.
But it booted in seconds, and it appeared to be perfectly clear. I hit "Display" on my X10 remote and it showed it was receiving a 2160p signal. Very interesting. The nature thing (something about flowers) was pretty and roughly on par with the 4K clips on the device.
Next, I hit "House of Cards" and went to the first episode of season two, where I knew there was a recap in 1080p before the actual episode switched to 2160p. Sure enough, my Display showed the clip was in 1080p (Super HD) before switching to 2160p. Now, this was impressive. House looks fantastic, vibrant, alive. It still didn't put me back on my heels, but I'd certainly prefer this to 1080p. The clip in Super HD was almost as good: just a pin-sharp picture. Checking out Hitch for a few moments didn't fare as well: there was noticeable grain.
I really have no idea why I can easily stream 4K content with such a pathetic download speed. There were two variables: I watched it around 11 am EST, when traffic is probably slow, and I have the X10 wired up via Ethernet, figuring wireless would only give me problems.
I still have yet to watch Monuments Men so can't comment on that yet. Overall, while I was pleasantly surprised to be able to stream 4K and find House of Cards to have a knockout picture, I might have to agree with people who say you need to either sit closer or have a larger set to truly appreciate the 4K difference. I realize that's been dismissed by some, but it's likely a subjective thing. For me, 4K looks like a truly excellent and well-calibrated plasma HD picture, House excepted. (That just looks like a more substantial jump, likely because it hasn't been scanned and was shot with 4K in mind--I think.)
If Netflix can continue to build a library of more modern films scanned in 4K and continues to offer original programming in that resolution, I think there's reason for excitement, particularly for owners with bigger sets. The Marvel shows coming in 2015-16 should look outstanding in 4K. For me, I got more of a "holy sh-t" moment from Netflix's Super HD streaming than anything. (Keep in mind I was coming from an 8-year-old Sharp 37".)
This really is an awesome, well-rounded set: great 3D, great sound, great upscaling, and great-looking. 4K is a fun novelty to play around with, but I wouldn't consider it a huge reason to buy unless you're really putting chips down on 4K being the future.