I'll get to the point and say: Do not buy the game now. There's so many better options now, including Battlefield 3
The core concepts behind Battlefield 2 are insanely fun. Conquest is easily the best multiplayer mode ever constructed, and the vehicles and planes on paper are great. Lots of classes, lots of maps, just insane variety.
Unfortunately, this is all spoiled by the HORRIBLE gun physics engine and poor aircraft balance which makes the game nigh unplayable.
The guns are so inaccurate, it's not even funny. You can expect the guns to actually hit the cursor about 25% of the time, and most of the time it will veer wildly EVEN on semi-automatic mode. The guns absolutely REFUSE to shoot in straight lines. You would at least expect the first shot to hit straight, but no, the guns have essentially zero calibration. Don't even think about using full-auto (even in bursts) at long range. The spread is plain ridiculous, the guns will randomly jerk after 3-4 shots in a totally unreasonable pattern.
To make matters worse, at close range the gun system totally breaks down. You would think that moving closer would improve accuracy, but NO. You can still expect to get only 25% of your shots at close range (