Besides an intense but rather short campaign, Call of Duty has a great multiplayer experience relying on infantry tactics. The maps lend themselves to a more balanced battle, with multiple ways to flank enemies and multiple strategic points. Those individually minded will enjoy modes such as Deathmatch and Behind Enemy Lines, while those who enjoy teamwork will like Team Deathmatch, Retrieval, or Search and Destroy.
Although Call of Duty has been released for about five years now, there are still a variety of servers and mods that enjoy much popularity, as well as a dozen or so clans. Have fun joining different servers and meeting new people!