One character gets a shotgun, which works like Half-Life's shotgun, and the other gets a stake crossbow, which can destroy vampires in a single hit. I'd prefer the shotgun at close range, even if it's not instantly lethal. Not only that, but the vampires can heal themselves by draining blood from the hapless slayers. The catch is that the vampires need to get close in order to do so. This latter ability is particularly useful for lunging from the shadows at an unsuspecting slayer.
Vampires are slightly harder to kill.
If not staked quickly, they are restored to life. Some of the maps have some really nice architecture and details. I should mention that the maps for Vampire Slayers accentuate the feel of the mod quite well. Since the vampires need to be able to get close, they need to either have shadows to hide in or lots of places to hide. All the twisty corridors made for confining battles that really gave an edge to the vampires if they took advantage of the layout.