Besides being one of the top-selling games of all time, I got my IFR airplane rating in the minimum number of training hours on the first test ride thanks to practising procedures with FS5. That $50 program saved me over $1000 in block time. 🙂
After MS stopped developing it around 2009, they licensed the ESP version to Lockheed Martin as Prepar3d, restricted for non-consumer use for around $200. In other words, it’s military-grade simulator software.
The rumor is that FS was Bill Gates’ “personal hobby project”, and that one year after he stepped down it was killed off.
If you can’t wait for FS2020, the free and Open Source Flightgear is pretty nice too, with photorealistic sky and terrain rendering. Some enterprising folks even box it for sale.