I dont have managed it to play call of duty under linux
But I have heard about that they want money in the future to play cod.
Make sure to check out wine forums for help about any windows game in linux. Also, all game makers are trying to get more money from gamers and their rich parents. The CEO of Activision sees a $50-60 becoming a $100-120 with the lame add-ons and no support for the modding community. This leaves you with 4 options.
1. Be a sucker and buy all the games with all their add-ons.
2. Pay for the original game, but only support hacked gaming mods (like the COD:MW2 dedicated server mod)
3. Pay for the original game, and stick it to the man by getting his $10 add-ons through less legit means (TPB)
4. Give up gaming and become a linux hermit/hermitess.
Personally I've decided to dedicated myself to 4. Though I do play games, but I have a lot more fun getting games work with wine. Besides, there are plenty of bugs that need hunting.