There was also a game (actually 2) released over 10 years ago, the first was RAPCON, the second TRACON. These were based on the US system of ATC.
RAPCON was mostly (all)military aircraft at several locations in the US, such as Pensacola, Edwards, San Diego (Mirimar etc), and also featured an Ground Controlled Approach (GCA) option.
TRACON was a later release (I believe) that was based on Civil aircraft and locations (such as Washington, LA etc).
Both were relatively easy to use, and you could select the weather level, pilot ability (sorry guys!) and traffic rate prior to starting the Sim.
If you wanted to get into it, you could also design your own airspace etc and run that using data from the Sim. We actually did this for a Military field I worked at here in Oz. Was not bad, considering it was running on a 286 machine.
Scran