OMG, you guys. What took me so long?
You have to be reading this stuff. It's incredible. I am totally obsessed with it, even beyond past obsessions with such other high-quality webcomics as Gunnerkrigg Court.
MS Paint Adventures is a gamelike, massively collaborative webcomic. Originally, the artist did one panel a day, in which the main character would perform and action that had been suggested by an audience member. Now, the comic has become so successful that its original model doesn't really work anymore; the whole forum crashes whenever the suggestion box is opened. Still, the artist, Andrew Hussie, does take heavy inspiration from ideas brought up in the fan community. (He has also abandoned the pretense of using MS Paint; the most recent adventure makes liberal use of Flash and even incorporates music.)
If you've got no plans this weekend, I recommend you dive into Problem Sleuth first; it's a complete story, and will give you a fair grounding in how the comic works, plus insight into a lot of inside jokes in the current work in progress, Homestuck.
Read it. Love it. You're welcome, darlings.