First I'll give you what the developer has to say about the game. A direct quotation from EaGames.

BATTLEFIELD 2 PRODUCT DESCRIPTION

The award-winning Battlefield franchise invades the high tech frontlines of modern warfare in the new sequel, Battlefield 2a„?. The game brings the intensity and excitement of Battlefield 1942a„? into the modern era with enhanced team play and the latest, most technologically advanced vehicles and weapons systems available to man.

Ok. There we go. However, your in-game experience may be not what you expected.

Ranking
Battlefield 2 through official servers has what is called ranking. The more points you earn, the more you can advance in military rank.

Currently, you earn points by killing enemy troops.

The downside to this, and what makes the game a disappointment to quite a few players, is the effect ranking has on the quality of team play. Enhanced team play as stated by the developer to be specific.

You may choose to play on un-ranked servers but there may not be too many opponents to play against.

Effects of Ranking
Ranking has the unintended effect of causing a majority of players to defeat the concept of team play by being an incentive to accumulate as many points as quickly as possible at the expense of your teammates. Period.

Whatever features of the game which could be attractive, such as "the latest, most technologically advanced vehicles and weapons systems available to man" are offset by the
negative impact ranking has on the gameplay.

My Opinion
Battlefield 2 is less a game of team play than a free for all hectic dash to increase your rank in the game. A more clever approach would be to tie an individual score to the outcome of the team for the round played.