Spent a few hours with my 3G Vita, and a few games and here are some initial thoughts:
HARDWARE:Sony proves once again they're top notch hardware engineers. The physical build of the device feels very sturdy. So from nuts to bolts--it's just a wonderful thing to hold, and oh man that OLED is goddamn gorgeous. I feel like if I were to drop the device on my kitchen floor it would probably survive without cracking screen (not testing that!). I'm still not sure how the Vita will fit into my life--as I just got it--because I love it, but it's just not small enough to tuck into my pocket. It seems it'll be for couch while my wife plays SKyrim for the next 2 years and, of course, travel.
OS & UI: Although at first a little awkward to use, it turns out I really like the look and feel of the interface. It's fast, responsive and mostly intuitive once you understand the format. When you tap an icon to launch the game, it instantly goes to a start-up screen where there are links to start the game, read the manual, go get DLC (if available), visit the website (if available) and a few other things. Not all games include all the stuff, but in my experience most appear to. It doesnt feel cluttered or overbearing to me, and really apprecaite the digital manual thing.
Applications close instantly, with a simple press of the home button and a quick swiping--love it.
The screen treads downward as you install new software. Like iOS there are little dots along the side so you can see what page you're on. So far I have not found a way to remove icons though. When I put in my copy of Ninja Gaiden Sigma, is prompted to install (huh?) and did so in about 2 seconds and now the icon sits there even when the cart is removed.
The virtual keyboard layout is also very similar to iOS where the key you hit pops up over your finger so you can see what character is hit, and I like it. However the autocomplete isnt nearly as competent, but at least it's there.
Trying to set up the 3G account thing with ATT was a nightmare, but perhaps not necicarily at the fault of Sony or ATT. Though I already have a mobile account, I couldnt remember my login to the ATT website. Trying to reset my password sucked. The dropdown security menus to answer the security questions didnt work on the Vita. I tried various other ways and finally gave up. I tried for a good 30 minutes, mainly because I wanted SSDD, but eventually just spent the $15 on the game. It was worth the frustration (and wasted time, now that I'm a daddy).
Also, in the inital setup I had to login with a temp account to update the Vita firmware in order to get my regular PSN to work. But the fun didnt end there. Initially my account was recognized either, despite being 100% certain I was inputting the correct username and password. Heck I even changed my password twice on my PS3 to make sure of it! I was 2 seconds away from calling Sony support until I plugged the Vita into my PS3 and it prompted "would you like to use the current account on your PS3?" I said yes, input the same password I've been using and it connected--YES!!
Transfering all the games over (6) from my PS3 to the Vita was slow, but there was also 8GB of data to move (read: not copy). But the interface to do all this worked well enough.
(Note: I've not beat any of these games, this are initial impressions so my opinions could change!)
(9/10) Rayman Origins: The showpiece! This is the software you're going to pull out to show off what the Vita is capable of, and in particular how beautiful the OLED screen really is. But if you're not aware, Rayman Origins is cheeky and fun and worth the $40.
(8/10) Mutant Blog Attacks: An underrated, great game I hope people don't pass on, especially for the price. In fact it's probably tied with my second favorite Vita title (Super Stardust Delta). It's wacky, fun, easy to jump in and out of. It's like a 2D Katamari. You roll around collecting junk to get bigger, so it's got a puzzle aspect to it. Is it better than Katamari, I dont know because I've not played it yet, but it's a lot cheaper.
(7/10) Lumines: It's Lumines, but with more Electronic Symphony.
(5/10) Dungeon Hunter: It's ok, but not really worht the $40 they're asking. Pick it up when it hits $15-$20 unless you're dying for a dungeon crawler.
(3/10) Asphalt Injection: Pretty bland and boring. The graphics are mostly a bore (but hey there's lens flare!), the physicals model is mostly nonexistent, the car handling is mediocre, the female commentator talks to you like you're a horny 13 yr old boy and the music is lame. You drive a car and there are things to unlock and upgrade. Word.
(7/10) Army Corps of Hell: So far I really like this game. It follows in the footsteps of Pikmin where you have a bunch of little creatures who follow you and do your bidding. It's fun, gory and coupled with really bad 80's thrash metal (which I sorta love). Cool game!
(6/10) Ninja Gaiden Sigma Plus: If I'm not mistaken, it's a remake of a remake. It's not 60 frames and closer to 30, but it still looks great. I think purist might be a little turned off by that but I think it's pretty cool and kinda hard so far. If you like NG you'll like this IF you've not played Sigma.
(8/10) Super Stardust Delta: ...more more more SSD! I love it, and the controls, though a tad awkward at first, work well too. A fairly good looking game, great framerate and just so much fun.
...Still waiting to check out Uncharted, Gravity Rush (!), Hot Shots Golf, Virtua Tennis 2 and a few others I can't think of right now.
edit: updated some info and added some more opinion.