First of course, on the TV itself: it's surprisingly thin and light. It's actually only slightly heavier than my old 40", despite having about 1.9x the viewable surface. It was too physically large for me to put onto my wallmount by myself, but the pedestal is designed in such a way that I could just put it on that and then some time later I can just undo four screws and, with the help of a friend, put it on the wallmount. (Of course, my existing wallmount can take it; when I bought it I knew that I'd eventually be upgrading to something larger so I went for the largest capacity that seemed reasonable at the time.)
The display is really crisp and bright. The downside to it is that being very shiny, it reflects the light behind my couch, so I'm going to have to rearrange my living room lighting setup. Also, any sort of bright light reflects in the screen, and has an odd RGB halo around it.
It has a pretty good UI. It's one of Sony's usual "XMB-inspired" ones, but this TV actually has enough CPU power to make it run well. In a lot ways it's better than the actual XMB, too; when scrolling through long lists it gives tab hints on the left saying where you are in the list. Since every single TV channel goes into the "TV" menu, this actually becomes useful. (It would be more useful if it had actual names on the channels, and not just numbers and occasional FCC IDs for the digital stations.)
The built-in Bravia Internet Link stuff is pretty good too. It feels like a bit of an improvement over the stuff in my Blu-Ray player, which had already replaced my TiVo, which I had only been using for Netflix at this point anyway. (And the Bravia Internet Link has a lot more than that, too. It has a lot of excellent channels, as well as ties to blip.tv, Crackle, Qriocity, NPR, and more, and it will be getting Hulu Plus when that goes public too. Plus, it has a pretty good YouTube interface.)
Of course, the biggest thing about this TV (aside from the size) is that it's got 3D glasses support. When I bought it, I also got the 3D Starter Kit (which includes the sync transmitter and two pairs of glasses). There are two sources of 3D content that I already have: the PS3 and YouTube. I tried YouTube first.
YouTube's 3D content is in split-screen side-by-side format, instead of over-under. On the PC, the Flash player is capable of understanding the various format tags and converting it to a number of different display modes. The other platforms don't have that just yet, though; they can only show the raw side-by-side format. Unfortunately, the built in YouTube player on the TV doesn't let you set a specific 3D content mode (yet), but I could get a taste of things to come by playing it on the Blu-Ray player and forcing the TV into side-by-side mode. It worked pretty well! Unfortunately, most of the YouTube content is in square-pixel 8:3 or 32:9 (so things get squished horizontally), and most of the producers don't set the convergence properly, so it's a bit painful to watch long-term, but there's definitely a lot of potential. Hopefully the various embedded players will be able to get the YT3D functionality natively. (Hopefully it would also not be done in a way that causes the UI to get stretched horizontally and then split between the two eyes. Although that does give me an idea for a virtual desktop switcher!)
The TV also has some "simulated 3D" stuff which does some real-time image analysis to try to separate things out into depth layers. I turned it on for an episode of Fraggle Rock and it worked surprisingly well, but it did give me a bit of eye strain and motion sickness, so it's really more a novelty than anything else.
Now, the real reason I got 3D: games. The leap from black and white to color was a major change, and from CPU to GPU rendering was another major change. I feel like mono to stereo is another huge potential generational leap. Right now, all of the games which have made the transition have only added it as a feature on top of an existing game, and that's already making a huge difference in gameplay. Imagine what it'll be like when gameplay can actually make use of stereo vision for actual gameplay elements!
I already have several 3D-capable games: Tumble, Super Stardust HD. and Wipeout HD, and several more coming (for example, The Sly Collection will support 3D glasses). Many games with 3D gameplay have suffered from the lack of depth perception, so it's pretty obvious how 3D will help. And boy, does it help.
Tumble was just plain easier to play, which made it more fun. Without 3D, you spend all your time trying to figure out the depth (the shadow hints aren't quite enough). With 3D, you can more quickly build much more elaborate and interesting structures.
Super Stardust HD was more immersive and much more clear about what was going on. It felt much more natural to make long-distance shots when I could perceive the curvature of the planet shield at a more familiar level.
Wipeout HD didn't really benefit much from 3D visually, but it did make it a lot easier to judge the track curvature and anticipate my hard turns.
I suspect that Sly Cooper will also become much more playable; being able to judge depth in some of the more complex jumping sections will not be nearly so difficult anymore. I might actually even finish it this time around.
Also, I don't know if this is because of the 3D immersion or what, but last night I had an intense and kind of hilarious dream about Tumble. In the game you are simply stacking inanimate, not-at-all-anthropomorphic blocks up to fulfill various challenges. In my dream, the blocks were alive and conscious and had cartoon googly eyes and liked to jump around and interact back, and one of the challenges was to get them to all pile up onto the platform, with the twist that about 10 seconds in a huge stampede of them showed up and flooded the arena. There was a giant white hole in the background that I could fling them into, but after about 30 seconds, a giant Weighted Companion Cube fell and blocked the hole. But eventually we all cooperated and it worked out for everyone.
I'd played a lot of Tumble before and had the usual Tetris dreams about it, but I have a feeling that it was the step up to 3D that brought this up to the next level. The difference between seeing it and "being there," so to speak.
Now, there are a few downsides to any shutter-glass stereo 3D method, and to be honest, the HX800 does have all of them, to a very small degree. The glasses shutter at 240Hz, which is great when looking directly at the image, but during saccade there is a tiny tiny amount of visible flicker. Most of the time this isn't a problem, but in some high-contrast cases (such as the menu system in Wipeout), this can get a little bit annoying. During the game itself it's mostly fine, though.
The second problem is cross-eye bleed, where a little bit of the left image goes to the right eye and vice-versa. I have used many shutter glass systems in the past and they have all been terrible. On the HX800, there's just a little tiny bit, and again, it's only noticeable in high-contrast situations. It's never that annoying.
Finally, head tilt becomes an issue because the polarization of the glasses interferes with the polarization of the TV. In this case, it actually reveals a bit of how the new generation of glasses work; long ago, the glasses would actually flicker between transparent and opaque, with a dual-layer polarizer (one fixed, one liquid-crystal), but these ones appear to work by just having a single liquid-crystal polarizer, which toggles between unpolarized and perpendicular to the TV. So, if you tilt your head sideways, you end up seeing both images in both eyes. On the plus side, this is actually a pretty good failure mode because it eliminates the obvious source of eyestrain and possible injury in that case, due to your eyes trying to converge off-axis.
Also, one issue with the TV vs. Move gaming: Remember how the screen is reflective to bright objects, and adds a strange halo around them? Well, the Move controller has a bright ball at the end of it... Fortunately, during gameplay I don't seem to notice it.
My hope is that more TVs will support 3D in the future, that the price of the glasses will come down ($150/pair is quite a lot, although it's far cheaper than trying to use passive polarized glasses instead; who cares about $2 glasses when the TV costs 10x as much?), and that games especially will start to make innovative use of stereo vision features. I don't really care about 3D in the cinema or for TV, but for gaming, it basically leapfrogs over the old notions of "virtual reality" and makes something that's actually fun and entertaining.