It also successfully integrated tanks, artillery, jeeps, deployable machineguns, and had one of the best ideas for kill streaks I've ever seen in Multiplayer, plus there were no "perks" and you had to choose a faction-specific gun.
So dam tired of UAV this and airstrike that and helicopter here, it's half the reason I left CoD.
It was also pre-steam, so creating your own maps and mods was encouraged. CoD lost a lot of potential when they switched to steam, but I have no idea if it was because of steam or just a coincidence.