(Update: There's another new map in this update, Mountain Lab! Both new maps come from TF2Maps.net's Art Pass contest.)
Also new are fresh community made and Valve made items in the Mann Co. Store, some of which are only available while the TF2 Halloween special update is live. That's from today until November 8, by the way.
If you're at least this tall and don't suffer from a pre-existing heart condition, it's recommended that you start playing some Team Fortress 2 now. If you dare, of course.
Team Fortress 2 - Halloween Special [Team Fortress - thanks, gregfromtheinternet!]