I bought FS 2004 because "it was there"...!
I've got FS '98, FS 2000, FS 2002, and FS 2004, and in my opinion the most impressive up-grade was from FS 2000 to FS 2002.
FS 2004 incorporated a few changes of marginal interest such as the weather, but I find that the clouds are real frame rate hoggers, and are inferior in appearance to the more realistic, whispy clouds in FS 2002.
There are also many add-ons to vary the weather and water effects for FS 2002.
I find the ATC quite adequate in FS 2002 and together with FS Navigator works fine for me....

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The default aircraft included in FS 2004 are of little interest as they can be supplied by the various designers out there, (many thanks!)....

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So...
For these, and many other reasons, my FS 2004 sits sulking in amongst my pile of games programs, while I have fun with good-old FS 2002, it's excellent frame rates with everything wound up to the max, (autogen, weather, ATC, etc...), and all my many add-ons for it...

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Cheers all...

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Paul...a very happy bunny, FS 2002 user...

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...Who knows what FS 2006 will bring...

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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.