Pros: Accurate topography included, very pretty airplanes.
Cons: Needs a super powerful computer to operate satisfactorily.
The bottom line: Wait about three to five years to allow technology to catch up and prices to drop, and get what is today a top of the line rig.
I bought the hype so I bought knowing I would have to lower my settings a bit. I have a 2.53GHz P4, 1G RAM and an NVidia 7600 GS video card. I run FS2004 with MegaScenery and all sorts of add-ons with the sliders maxed out with no glitches whatsoever.
I was happy when I first loaded up FSX and went to my airport here in Reno and noticed that the terrain was accurate (I added FS Global to FS2004 to get the proper local terrain). I looked around from the cockpit view and noticed that there were no buildings whatsoever. After taking off and looking down, there was a 2 dimensional landscape that I guess was supposed to be the city. Picture every city on earth shoved into the ground with their rooftops even with the ground; that's what this program was like.
I then tried Las Vegas, notably because even the default scenery in FS2004 was so extensive. No joy in FSX...flat as a pancake. The surrounding hills, canyons and valleys are there, but no buildings! Once airborne, you can see a 2 dimensional version of The Strip. At this point it flew well with a bit of stutter.
I then went into the preferences setup and all my sliders were set to minimum. I turned up the scenery to halfway and tried again. After finally loading up (it takes a while), I noticed buildings. I clicked my view switch to look out the left side and it stuttered into position and just froze. Went outside and had a smoke, came back and it was locked up tight.
I have since removed it from my machine. Unless you have a Cray computer or can afford big bucks for today's top of the line PC with dual video cards (probably $4K ), it will drag on your machine with anything set much past minimum. Save your bucks and stay with FS2004.