When you think of Battlefield - you think of a specific type of gameplay.
Without a doubt, now a day gamers are always looking for something new or improved. In many cases, sequels or revisions of games change too little or too much. Battlefield 2's success should give a good impression of how well EA undertook the challenge.
I believe one of the strongest points of interest relates to rank and progression in the game. Certain weapons are restricted for all new players, requiring said players to attain better rank in order to unlock their next means of destruction. Not only does this encourage good players to continue playing well, but it also encourages those who would normally be apathetic towards their team to pick up their weapons and work towards a common goal.