BF2 is mainly a multi-player game and momentary the only game I have installed on my new HighEnd PC, I play nearly each evening some on-line matches with it.
Sure it has a single player option but it is from my point of view only a training session, expect no good AI of the CPU controled units. But the single player is well to learn the handling of the different units and weapons
And there are great multiplayer WWII and WWI mods in development