Well yeah, just finished the Eternal Damnation Mod for Postal 2. Somehow I missed that one over the years and just recently discovered it.
It's more of a total conversion thing.. it has its own story, soundtrack, voice acting, weapons (lots of) and is so totally different from the original game. You're basically playing some horror/zombie kind of shooter.
I'm not too good at descibing it but if you're into horror/zombie stuff you should check it out. I enjoyed it for the past days. Very well done.
Download is over 1GB but well worth. Check out the Mods/TC page for links.