Yeah, it's great. I think Idol originally told us about it, and I used to play it quite a bit. Essentially the cap for the server is nine people. Eight are members of an assault team, and the other is The Hidden - Some sort of killer genetic experiment gone wrong. Basically, this guy is invisible, can cling to the ceiling (and maybe walls), and kills the hell out of people.
The assault team picks a load out consisting of a main weapon (machine gun, shotgun, etc), a secondary weapon (pistol), and a third item basically to make it possible to kill an invisible enemy. I think the options are some sort of proximity sensor, trip wires, night vision, a flashlight, and a laser sight.
The Hidden gets a knife and some pipe bombs. The pipe bombs do tons of damage, and the knife can either be used to slash or to "pig stick" someone in the back for an instant kill.
Things get fun with 6 people in and one suddenly dies. The next 10 seconds are a bit of a blur of friendly fire, things (including bodies) getting thrown at you, and the sound of a knife cutting through air. Next thing you know there's only two of you left and you hear someone whisper "Fresh meat..."