Portal
Pure dumb luck led me to find a PC version of The Orange Box on sale at Amazon, and so now I've finally got a copy of Portal I can call my own (along with the box's other bajillion games). Of course I knew I would be able to play through most of it in a single sitting, and I've already watched my friends struggle through the game so many times that it wasn't really challenging at all. But it's still super-cool.
Progress: Testchamber 19