FSX was the first sim to truly nail the feeling of a world in motion. You will see other airliners taxiing, ground vehicles pushing back planes, and wildlife on the runways. Even today, the default airport activity feels "busier" than many modern competitors that rely on external add-ons for this feature.
One of the defining features of the Deluxe Edition was the inclusion of the glass cockpit suite. This integration allowed players to fly modern aircraft like the Cessna 172SP and the Beechcraft Baron 58 using an accurate digital avionics interface. For aspiring pilots, this was a revolutionary educational tool, as it mirrored the transition the real-world aviation industry was making from traditional "steam gauges" to integrated flight decks. Microsoft Flight Simulator X deluxe
But that grit is part of the charm. In FSX, you feel the landing. You struggle against the autopilot. You celebrate nailing a VOR approach because the instruments are all you have. FSX was the first sim to truly nail