I enjoy a good game of Call of Duty but I also enjoy a game of Battlefield or Halo. I enjoy these games for different reasons and everyone will have a different opinion. Call of Duty, even if you're playing a team game, is a lone wolf game. Even in Team Deathmatch or Team Slayer, everyone is competing for the kills. The fact that there's a kill limit really increases the competition. In Battlefield the games aren't necessarily based on kills as it is a class based game. The multiplayer is split up into different classes that are meant to perform different tasks to benefit the team. By introducing tasks that don't involve killing, the game turns into something a bit more sophisticated. By not even showing the amount of kills, assists, deaths and kill death ratio, it changes how the game is looked upon even more.
Halo may have games like Team Slayer and Lone Wolf game modes but there are more team based games that are actually team based. Doubles requires a lot of team work to effectively eliminate the other two enemies. In Halo: Reach, with the introduction to jet packs, sprint, evade, active camo and armour lock it creates even more team work, different people who are good at different things need to choose the best load out to achieve their goal. A sniper might choose a jet pack to get to high places or active camo. A player who likes to rush might choose sprint or evade or even armour lock. Halo and Battlefield and other games like Homefront (a game that I have no intention of playing) all have vehicles, something that Call of Duty STILL lacks in it's gameplay.
The use of vehicles creates a sense of team play, especially in Battlefield, one player in charge of something, the other in charge of another thing. Personally the best game that has mastered both of these things is Halo, it has the team work part in some game types and has other game types that suit solitary players but in the end I would take a game that takes team work and communication, like Battlefield, over Call of Duty. It forces you to communicate with other players and actually use a strategy and use your skills to complete the objective. I would love it if games started to meander to the team work side of gameplay but there will always be games like Call of Duty that live on, I can only dream that a team based game will be the next COD killer.