Microsoft Flight Simulator is one of the oldest and best flightsimulator products in the area of flight simulation. Due to its extensive use of plugins and addons it can easily be extended to a much more enjoyable state.
Though it's named v5, this was a really big release featuring a completely new weather system (storms, 3D clouds and fog) and a lot of performance and graphics improvements. This was the first version published on a CD-ROM. Its sequel (95) was a windows port of this DOS version.