Fallout 3: Point Lookout

Wow I did not know what to expect going into this one but this is my favorite DLC for Fallout 3. It's short and sweet. You show up to a pier and looks like the Jersey shore and then you go off exploring and find it's mostly swamps. Then you start fighting the hillbilly mutants and realize you're in Louisiana. It's got a fun plot about two ancients from the old world, one a ghoul and one a disembodied brain with telepathic powers fighting each other in a longstanding rivalry with you caught between. Also caught between is a tribe of borderline troglodytes under the sway of the brain guy.

All of those things sound amazing to me but what sold me was the writing for the characters. Desmond, the ghoul, is a foul mouthed asshole. And one of the few ghouls you meet who makes sense. Because after living for 200 years why wouldn't you be one of the most badass entities on the planet. To survive that long takes some serious skill. Plus you would in all likelihood become a real asshole. That and the girl you're supposed to save turning out to be a badass herself, finding out the guy who ferrys you over is none other than the guy who does a basic brain surgery on everyone who joins the tribe. Oh man it was so good.