Haven't bought it yet, but playing around with it in the store tonight here's my notes:
1) Nice screen size - finally getting bigger and closer to what's optimal for those 800x600+ resolution screens they've been tossing into smaller phones (which we can't read well at all due to tiny fonts). Here, even small fonts used in portrait mode to view Engadget's main left side posts, zoomed to view width w/o scrolling sideways, is readable and nice. crisp fonts. makes you wonder where have bigger phones been all along.
2) Blows Android phones out of the water.
For awhile, all that flexibility to have multiple desktops, movable icons, etc. was cool. But after awhile, why do things always move about? Why can't things stick in one place and just be? why are load times feeling a touch sluggish? ie. you spend a lot of time 'mousing' around the desktop, but not really getting any for that movement.
Well, this baby is the reason. Responsive - like a fast desktop fresh out of the box. Icons scroll through under your finger on the main page like they were connected to your mind. HTC customization is cool and intuitive. (and, it's like customization? do I even care anymore where my icons are? Everything HTC has done makes it seem like an integrated Borg cube flying outta nowhere to assimilate the masses. Feels faster than Androids I've seen changing heavy apps, loading heavy pages, etc. Engadget loads up so nice, it's like well, welcome to the 22nd century!
3) TV works. Not true HD, but more like the usual 320x240 or whatever streaming IP TV you see. Hopefully, once TMo turns on 4G everywhere, they'll have HD TV.
4) Transformers.
Can't say there wasn't some sort of lip sync issue with the demo on the one I played with, but there was a little of it. Soldiers in the control room saying things, sound not quite moving with them lips.
Otherwise, only thing you could ask for is a super-bright backlit or OLED.
5) Screen. Crisp. Simple as that. You can read 2pt font on this baby and it still feels like there aren't pixels on the smooth screen. Just images. Could be brighter, but I'm too used to super-bright LCDs on desktops....
No problems reading anything anywhere however, so probably bright enough for indoors.
6) Youtube. Works, a little load lag due to the network, but otherwise, nice to see full screen streaming at a size that's more comfy for handheld sharing and viewing. Makes you wonder why all phones dont' have screens this big or bigger by now.
7) Glossy front. Fingerprint magnet. Impossible to keep clean, now makes you wonder Touch Pro 3 with 5" screen and sliding keyboard, please! It'll be messy screen, or messy shirt. Your pick. You'll still have to wipe off the screen now and then - eventually, it'l interfere a touch with input (like most touch screens).

Feel, thickness, heft.
Near perfect heft. Thickness is just right. Feel is rock, titanium, something solid. Nothing that'll make you think you'll break it using it at all. Nothing odd or out of place here.
9) zooms and views photos taken by camera fast enough. No lags out of the ordinary, just works. Nice.
10) Well, that said, compared to the sickly Neuron, it's a rocket. screen is nice enough to pick over any smaller alternative, and smooth interface and reponsiveness is so attractive. This is the first phone I've seen on TMo that makes me want to go home, save up more, and come back. (Other would be unlocked, like Nokia N900. But that's a different beast.) Despite the Windows 6.5 given the super nice HTC makeover. It's also a game changer in that all those tiny phones on display now look and are tiny. It's so comfy viewing heavy sites like engadget, you just don't want to go back to a smaller screen anymore ... on any smartphone... simply because you can view sites, not squint at them.
Anyways, downers:
1) No keyboard. still not anywhere as fast and sure as a real keyboard.
2) some apps do mess up. Mobi.TV dropped out once loading a channel, had to restart it. fussy. but that's like saying Windows doesn't crash... right? ha ha...
3) makes you itch for an even larger screen. Like why not 5-6"? That'll be nice! Easily fit into a pant pocket.
4) brighter. no idea why they don't put some more LEDs back there, but I want something that'll shatter eyeballs with bright, saturated eyepopping screens. But guess you watch nice TV sets too long and you think you're cell phone should be the same.... still, no reason they can't have it in there.