My friend and I began a Fallout 3 playthrough where we're going to play one character as both good AND evil. Like Dr. Jekyll and Mr. Hyde, our protagonist shifts from being good to being evil approximately every 10 minutes as my friend and I pass the controller around. And we're recording the footage (w/ commentary) and putting it on YouTube.
It's been fun for us, and has allowed me to come back to Fallout 3 in a fresh way after completing the main storyline. I was thinking about getting Point Lookout and taking our character over there since it looks like some pretty cool DLC.
The playthrough is being documented here: http://bosscast.wordpress.com/2009/07/18/fallout-3-playthrough-launches-us-into-the-apocalypse/