I've got all the versions from FS'98 to FS 2004, and for me the greatest improvement was the jump from FS 2000 to FS 2002.
Over the years I have spent time, and some money, up grading my FS 2002 to the stage where I now prefer it to FS 2004...

...!
It really has all I need in a flight sim as a low level VFR pilot, with the exception of a slightly better/more realistic texture at ground level.
If I could have grass texture similar to this at my farm strips, I would be more than happy, I've got everything else thanks to the many freelance designers out there...!

Cheers all...

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Paul...watch out for those mole hills...

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Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.