Every flight sim has its essence Viper. Handling the view system of different ones and knowing the vagaries of the flight modeling and gunnery modeling for individual aircraft in-sim counts for as much as knowledge of general ACM principles.
For instance, if I remember CFS correctly, as compared to AHII, you almost didn't use the snap views, they sucked, you used padlock, blackouts were alot harder to come by, the guns were much less effective, you could usually pull the stick back to the stop without consequences, and Spitfires were absolutely unbeatable. If that was your only previous experience with a WWII flight sim, welcome to the promised land.
