Couple of days ago, bought the potato sack.
Comments on the games I've played so far:
1. The wonderful End of the world - You eat stuff, and get bigger, then eat more stuff, and repeat. Very short, but thoroughly enjoyable.
2. AAAAAA Reckless Disregard for Gravity - Jump off high buildings, dodge skysrapers etc. Incredible fun, about as good as the real thing I would suspect.

3. The Ball - You are paired up with a big Ball and use it to solve problems. The problem solving is kinda Portal-esqe in style, which I love. The being chased around by monsters is not so Portal-esqe, and is pretty scary.
4. Defense Grid - Basic tower defense, but it feels highly polished. Good fun, but haven't played it too much yet.
5. Killing Floor - Again, haven't had much chance to play this one yet, but it seems to be interesting enough.
6. AudioSurf - IMO, the best "game" in the pack, and one of the most enjoyable "games" I've ever played. However, I wouldn't view it as a "game", I'd look at it as a way to enhance listening to music. Just load up a song you like, and you're off. I've been playing through a selection of songs I like, and its just been tremendous.
7. Super Meat Boy - First off, fantastic presentation. Everything about this game makes me want to love it... except that I ********** HATE IT!!! The most irritating experience of my life, but not one to miss.
There are 6 other games I haven't gotten a chance to play yet (well, 5 actually. I set out to play Amnesia last night, but thought better of it after 10 minutes.) Anyway, I've been really impressed with the games I've played so far. Worth picking up before the sale ends.