If any of you ever played Heavy Metal map on BC2, you'll notice how no matter how good you are, you can't win a game without teamwork and strategy. Holding the anti-aircraft gun in the mid flag, pushing forward with armored tanks, holding points and dropping off guys behind the flags to hold them, taking out snipers hidden in the forests, taking cover and using infantry to take out soldiers in buildings.
I like that every role seems realistic enough that its fun, where infantry can still dominate tanks in enclosed towns and buildings while being owned by them in flat terrain. Where you can still take out people hiding behind buildings and certain types of cover, and campers don't live for that long if a team knows how to find them. Where air support is useful only when you have taken out the anti-air forces, both vehicular and personel. Its a lot of strategy and theres so many different ways to play it.
Of course being too realistic is not all that fun either; look at Operation flashpoint: Red Dragon rising, its pretty realistic but who wants to spend 45 minutes (real time) driving to a battle only to die in one hit from some sniper somewhere.