The best Flight Simulator on the market
The sound is realistic, the graphics are nice but a bit dated as of now, but when it was released it was very nice, especially if compared to earlier versions. The virtual (3D) cockpit is really nice, though a bit ugly with the throttles and buttons you can't use since they are blurred.
The historical planes and flights are of course nice to have but don't really interest me that much. The historical value and what you learn is of course good but as for deciding to fly the Wright brother's plane or Learjet... there is no question for me, Learjet all the way.
The third party content is enormous and there are thousands of planes for download on the web, both freeware and payware. Not speaking of which, the ATC functions are cool too.
The only let-down is the multiplayer support, I tried it once but was disappointed, though I've heard this will be fixed in the new version.
It covers the entire globe and has more than 24,000 airports. But if you should buy it now, no, don't. Flight Simulator X will be released in a few months and it seems a LOT better.