Get really good at COD4, then join a good clan. That's what makes the game fun for me.
I'm in a clan that's top 10 in several ladders and #1 in a league. It makes the game so much more fun when your undefeated record is at stake.
The same would go for Battlefield 2 as well. Get in with a good clan that use ventrillo or team speak for comms and it's a blast...
