OK, so here is what I have in mind.
A group of assassins for hire, have to take out various people on a list. Then you have Interpol agents trying to catch these assassins. On top of that you could also add in CIA/MI5/Mossad operatives who want the assassins dead. The intellegence operatives would depend on how many people join in, but I think we need a 1:2 ratio of assassins to agents. Then member permitting maybe a 2:1 ratio of assassins to operatives.
Basically I copy and pasted that from a forum in which I started it on. I have enjoyed it quite a bit, but have ended up rewriting, and toning down quite a bit of my posts. I would like to get one going on here, and will most likely put it in the extreme section, just because of the possibility for excessive violence and gore.
Really it will allow for any sort of law enforcement character.