The MP is long dead due to the amount of different DLCs that breaks up the community.

I'm not even sure if the MP still exist today after THQ and Gamespy's death because I recall this game is using Gamespy service as well.

The SP is fun but the most awesome part of the game is the MP.

Nothing like gunning down a group of ppl as the Devastator with heavy bolter, roll out of the jetpack stomp shockwave range as a scout and gun down the guy with a bolter or smashing 3 people with the power hammer after jetpack stomping them.

No any other game has MP that fun, visceral, intense and satisfying.