Good Live Arcade FPS?

What is a good Live arcade FPS that has good multiplayer with a decent population? Besides Counter Strike and Gotham city impostors.

I can't really think of many others besides the two you mentioned in terms of new games.

There's Perfect Dark, Doom, Duke Nukem and Marathon which are great classic games, but I'm not sure if the population is there at all, it's been a while since I've played them.