So. Worm is wrapping up, and I thought I'd put in a plug for it. Epic, epic web serial, over 1,500,000 words in length. It starts out being about a bullied girl with a seemingly minor superpower, and ends up being about the fate of the human species, with lots of twists along the way. I'm not usually into superheroes, and I thought it was fantastic.
It should probably be the equivalent of R-rated for violence -- the author says PG-18, but I think he's erring on the side of caution there -- but my biggest warning would be that it's really compulsive reading and there's a lot of it. Be prepared to force yourself to stop reading. Repeatedly. It took me about two weeks to make it through the archives, and I didn't do much else with my free time during those two weeks. But yeah, I still recommend it. :)