BF2 didn't really have single player; same for 1942, Vietnam and 2142. I remember the single player modes were just bot matches.
BF2 Modern Combat on the PS2/Xbox/360 was the first Battlefield game to have something resembling a single player game. It was still a bot match, but you were some magical battlefield ghost who could inhabit any friendly soldier. So if you were a ground unit and saw a helicopter, you could transplant your consciousness into that helicopter pilot instantly. Bad Company 1 had an actual campaign, but the maps were still fairly open and Battlefield-ish. Bad Company 2 was Call of Duty. Battlefield 3 is Call of Duty.