I have FS2002 Pro. I can't compare it to any other flight sim on the PC as this is my first. I can say I don't regret shelling out the $$$ for it.
* HD hog
* you'll need a great PC to get anything close to decent fps
* landscape graphics ok, nothing outstanding
* plane models look awesome inside and out
* options up the yingyang
* great force feedback effects (recommend force feedback joystick with all 3 axis)
* mouse/keyboard flying is a joke
There are mods all over the place. My personal favorite site is
http://www.flightsim.com
They've got more planes than you can download (I've burned 4-5 CDs full of zip files), sound mods, panel mods, terrain meshes from USGS, real and ficticious locales, boats, cars, motorcycles, tanks, etc, etc...
You're obviously into flight sims so I have no doubt you'll enjoy it. I personally prefer Combat Flight Simulator 2, as I tend to get bored just flying around. I'd rather blow shit up!