I don't know if any of you guys play point & click adventures online much, but this series is probably one of my favorites. They're puzzles where you have to escape [whatever] using whatever you can find, but these have got some of the best atmosphere of any I've played (some seriously cool yet simple sound design).

JayIsGames.com announced that Part 4 came out this weekend, and I managed to beat it (though I needed to consult the spoiler to find one of the bonus "secrets", got the rest on my own)

Give these a try.  SumMachine 0 is the easiest, followed by SubMachine 1.  4 is easier than either 2 or 3, and personally I think 3 is the trickiest.  Highly recommended.

Artist's site: http://www.pastelstories.com/?page_id=17
Jay Is Games entry: http://jayisgames.com/tag/submachine

PS: if you play the first one, try to play the "remixed" version - it's a little longer and has a few more puzzles.

These games are brilliant. The story always confused me, but the puzzles definitely more than make up for that. The sound definitely made the game that much more immersive and involving :)

First run through, 19/21 secrets. I can't find the last two, but will look through a walkthrough at work. One or two were REALLY cleverly hidden, I must say...

This one, uh, brought up more questions than it answered, I think :huh: It certainly seems that its to be the final one, though. Bummer :(

EDIT: Speaking of sound, is it just me, or did the sound on this remind anyone else of Ex Mortis? I shuddered just getting through the walkthrough :o

Rumor has it there will be a 5th, only you'll be working for the Lab.  Nothing confirmed though, but I'm hoping so.