I dont mean pure graphics innovation but just like features in the game.
Built in VOIP
Commander feature who can call artillery strikes, drop supply crates, place UAVs, etc
Can fly jets, helis, boats, drive tanks, Humvees, all kinds of vehicles
64 player battles on pretty expansive maps
Unlockable weapons based on ranking up (CoD anyone?)
Booster packs (precursor to DLC, except they were more than a few maps)
Realistic graphics and weapon sounds
I could go on but its funny how much the FPS genre has regressed IMO. All these features were in a game that came out in mid 2005 yet MW3 sells out the ass and that game is boring to all hell if you ask me. So many different shooting lanes and wacky respawn points. At least in BF2 you picked which control point you spawned at.