Bad Company 2 was top tier for me because of how much the Battlefield itself changed over time, instead of being the same stale/stagnant maps over and over again. In most first person shooters, any change is only permissible by the amount of "power-ups" or weapon load outs (Which could be abused) chosen by the player. I'm not even going to mention scripts or "on rail" sequences.
BC had/has its fair share of disadvantages like the ammo crates you could post up next to in order to turn yourself into a grenade (M203) mortar launcher, C4 glitches and etc but the sheer scope/scale of each Battle really gave the player a chance to try out different tactical approaches to a map, whether in a vehicle or not. And like any FPS, if your team sucked, you were going to lose horribly.