Running a game where things have an expiration date, there's going to be an ending, and getting there is the fun. So freeing. I can take risks and do things I could never do on a static, ongoing game. I liken it to the last season of Breaking Bad - everyone is fair game and anything can happen.
Having players who can keep IC and OOC separate helps. They all know they're probably going to die by the end and gleefully do all the things characters in horror movies do, rather than play it safe and stockpile XP to become a demi-god. Even better, they signed up to be fucked with, and the more fuckery that occurs, the more they enjoy it.
So awesome.