The CoD line of games are fun if you enjoy games with a faster pace and a smaller emphasis on teamwork. But the battlefield line of games are fun also, just need to have a good team to do good because more strategy is involved.
If you have an xbox 360 then I strongly suggest you get Halo:Reach. If you are a PC gamer then get Battlefield Bad Company 2. If you are looking for a free FPS game then get Alliance of Valiant Arms.