I would like the challenge of having more movements per rwy per hour. Im guessing the game is programmed to randomly give out a certain number of aircraft per hour, and it seems like its based on availiable rwys. How about a possibiliy to select movements per hour before starting the simulation, so that you could try to play a very hectic single rwy airport for instance.
Also, sometimes two arriving aircraft enter the screen very close and at the same altitude. Perhaps this could easily be fixed.