You play as either slayers or vampires.
Slayers;
Meatbag - these guys generally suck.
Reaver - dual barrel shotgun with a stuff model
Hellion - big flashlight toting guys. they have smgs too
deadeye - insta kill crossbows if headshot, can use crossbows as grappling hooks.
All classes carry holy water, alt - click to restore health, left click to throw and ignite vamps.
vamps must be staked or they will come back to life where they died.
Vampires;
Fiend - really fast guys, can crouch jump really high
Gore - slow moving guys that can turn invisible by alt -clicking, super strong and cheap
bloodbanks - most balanced vampire class, they can move fast, have a harmless crouch jump, and can shoot blood with alt -click
All vampires can restore health and blood by pressing "use" on dead humans. if they crouch for a few seconds they turn part way invisible, this skill is useful, but moving will reveal yourself again.
This mod is pretty fun despite the fact that its only unique weapon, the dual barrel shotgun, has a stuffty model. Only about 20 or so people play it right now (myself included) so please give it a try :D
link:
http://www.moddb.com/mods/coven