MS Flight Simulator used to be good, but is now seriously outclassed by its competitors. Check out IL2 Sturmovik.
IL2 isn't the same class of game at all as Flight Sim. Do you have air traffic control in IL2? Real landscapes, cities, airports and planes? IL2 is a combat sim. Flight Sim is a huge, awesome flying sim.
I have a number of friends who are real pilots / ATC's and they use Flight Sim to get themselves acquainted with new equipment before beginning training on it (generally to find out if they like the plane first).