So far the game is looking really nice, and I know that you have many more plans. In case you have not thought of it, it would really add to the atmosphere if you added marshallers (the guys with the bright orange stick who guide the planes into the stands) and push-back trucks (tugs) for getting planes out of the gate. Further down the road, I would suggest adding the option of opening an aircraft maintenance facility as an option. This would give the CEO another way to make money for the airport, as well as another fun logistical challenge.
Andrew