So I installed Windows 8.
Windows 8 Xbox Games (IE games with achievements and Xbox Branding)
1. 4 Elements II - $5 Casual game that's one part adventure-light hidden object, but mostly plays as a sort of bizarro match-3.
You can see the gameplay on the Steam Greenlight page. The presentation is really lame, like a free online web portal puzzle game. I can't say I saw anything in the demo that merited a purchase.
2. Adera - Free. Killer App This is a great, really well-presented casual adventure game with a wide variety of puzzles, a nice and interesting plot and characters. It's going to be an episodic game, but I understand that new episodes will be released inside this same application. I got about an hour and a half or two hours out of this game. There are a bunch of collectibles, a bunch of different kinds of puzzles. It's pretty self-contained (most inventory puzzles play out within 1-2 screens of the place where you find the items, item usage is pretty much elementary and doesn't involve any fancy combinations or unintuitive usages). It's got a good hint system. It's got a female lead and is definitely designed to attract a wide variety of audiences, male and female. I really, really liked this. One note--the game's default camera is swipe to look around (I think there's an accelerometer option as well), so again this is an example of a game being built for tablets. It's mostly okay using a mouse but it's clearly a sort of afterthought.
3. Microsoft Mahjong - Free. It's Mahjong Solitaire. Several different variations, plenty of visual themes, achievements, medals (a bonus/secondary achievements system besides the Xbox Live achievements), daily challenges. Every few games you play, you're forced to watch a 30 second ad.
4. Microsoft Minesweeper - Free. Minesweeper, but with lots of different visual themes and a cool new mode they're calling adventure mode. Adventure mode is basically a dungeon crawler that takes place on a dungeon/Indiana Jones-themed Minesweeper board. I can't really convey this fully, but it's pretty neat. The game features achievements, medals (a bonus/secondary achievements system besides the Xbox Live achievements), and daily challenges. Every few games you play, you're forced to watch a 30 second ad.
5. Microsoft Solitaire - Free. Klondike, Spider, Freecell, TriPeaks, Pyramid. Includes lots of different visual themes, achievements, medals (a bonus/secondary achievements system besides the Xbox Live achievements), daily challenges. Every few games you play, you're forced to watch a 30 second ad.
6. Hydro Thunder Hurricane - $10. No demo, didn't play.
7. Reckless Ultimate Racing - $10. Didn't play, looked like a crummy racing game.
8. Rocket Riot 3D - $5. It's an updated version of Rocket Riot, a great XBLA game that works like a real-time jetpack powered version of Worms with cool pixel art and a great sense of humour. This revised version features extra levels, characters, and modes, and more involved game stats, which is a great improvement. Unfortunately, the game was designed to be played with twin sticks, and it doesn't work half as well with the default WASD+Mouse aiming. It's not the aiming that's the problem, it's the firing--the XBLA version makes you flick the right stick to fire, and the duration of the flick affects the power of the shot. The PC version has you hold down the left mouse button to power up your shot and it doesn't translate very well. I highly recommend the XBLA original, not so much this one.
9. Taptiles - Free. Square tiles are arranged in 3D space--unlike Mahjong, the tiles can free-float wherever. You can rotate the space by 90 degrees using the keyboard. You click any pair of tiles, like Mahjong, to remove them. You can only remove tiles with a free edge. There are a variety of modes including a time attack type mode and specific challenges. I like the visuals, really great Popcap-ish presentation as you play. It's a bit repetitive. One of the modes allows you to get extra time on your clock by watching paid Ads. Features medals (a bonus/secondary achievements system besides the Xbox Live achievements), and daily challenges, which are pretty cool.
10. Wordament - Free. Faithful port of WP7 game. Basically, it's Boggle. There's a 4x4 grid of letters that you use to spell out words. You get points for longer words, higher value letters, etc. You play for 60-90 seconds, simultaneous to everyone else on earth at the same time. At the end of the round, you see your comparative rank. You can play in multiple languages. It's a really great game with a great presentation. One drawback: it's less enjoyable to play with a mouse to highlight the letters than using a touch-screen.
There's also a Fruit Ninja demo which points out it's going to be updated with Xbox Live support soon. There's also Pinball FX2, but I'm pretty sure it's a 1:1 port of the XBLA version.