A web-epic told through illustrations, flash and most importantly lots of text. Easier followed in serial than as an archive, Homestuck is the most recent and by far the longest story on MSpaintadventures.com AKA: MSPA.
The story picked up a lot of fans when it started telling the story of 12 secondary characters, who became popular with the con scene. Probably because of their personalities, which are intentionally architypical, especially to begin with, and their association with the 12 western zodiacal signs.
The whole story is in acts, and the first and shortest is so uneventful and reader driven that it scares off a lot of people. When the reader base was small enough that it mattered the stories were shaped by reader submitted prompts, but when the reader base got large enough, Andrew, the writer and artist, decided that since he could just wait for someone to suggest what he wanted to do he'd cut out the whole process and just get ideas through the community in less direct ways.