I didn't even have a computer up until maybe 2000 or so, and therefore my first CFS experience was the first Microsoft Combat Flight Simulator. At that point I'd had a little experience on other people's systems, but most of it was spent in gravity- and liftless sci-fi "flight sims" like X-Wing.
After MCFS 1 I picked up on the civilian flight sims, then FlightGear, finally settling for MCFS 3 for a year or so. I later discovered LoMac and Aces High II, the latter of which is mostly an MMO WWII sim (I'm surprised I don't see much of it on this site, by the way, because it's really quite good).
Now I play mostly LoMac and Aces High II, with little else in any PC gaming category with the exception of Call of Duty 1 and a few select RTSs.