If you are reading this, then chances are you already know a little about the game and its good points, so I do not feel the need to list them here.
Of course the game is a little dated now, I switched over to this after taking a litle break from Enemy Territory: Quake Wars.
The first thing I noticed was how inaccurate and useless the guns were, compared to other games I have played. I was told that only the beginner guns are like that, but they just do not feel natural. In Quake Wars, my accuracy was often in the 29%-35% range, in this game about 14%. I gave myself plenty of time to try and get used to it, but was just unable to. Also, to compensate for this, you can prone (lie down) to get a better accuracy with your weapons, which you pretty much have to do in every firefight. Imagine you are running around a corner and are surprised by an enemy. What would you do? In Quake Wars I would back up, start strafing and pop them a couple of times in the head. Problem solved. In BF2, both of us would immediately prone and try to machine gun each other down from a distance of 10 feet. Personally I like my one-on-one fights standing up, where it takes more skill in aim and movement to get the kill than it does to be the first one to prone and keep the mouse button pressed...
Next, the game has a critical flaw which allows people to spam grenades then resupply themselves with more, thus getting huge spawn kills from their infinite supply of grenades. This is amazingly annoying, you get killed repeatedly in the same spot by the same guy and you don't know where he is hiding.
Finally, you get to keep your weapon upgrades. This has the good point of giving you something to work for, but the bad point that newer players will get steamrolled by the regulars, regardless of skill.