I always thought a dynamic campaign would be good. Anything can happen during missions, you might go on a patrol and find nothing, and whilst returning to base you run into a tank battallion heading towards the base.
Yes, it would be nearly impossible to do such a thing(although it has been used in Flight Simulators like Falcon 4.0, where events including ground forces occured in real-time around you).
Maybe randomizing missions? Give a number of different events that randomly get added during the mission would be good.