In a nutshell;
* Its a totally different sim compared with FS. It does not have certain things that FS has, and it has certain things that FS does not have. Examples;
1. Does have cloud shadows
2. Can add photo real scenery
3. Does have weapons systems
4. Does have actual aerodynamics through sophisticated seperate aero models that interact in a true aero virtual environment, great for engineers.
5. Does not have realistic ATC control (sound is like a robot instead of a humans voice)
6. No AI planes
7. Has cars and trains as ground traffic
8. Has tons of Autogen Scenery, perhaps double of FSX
9. Does not have buildings at airports like FS has
One thing that keeps XP9 people from coming to FS, and FS people from going to XP9, is the controls (keyboard inputs). The two sims are so totally different, that the people that start on one sim, who migrate to the other, simply give up (most of them) concerning being able to learn the new sim.
A for instance on this is the S key in FS. It goes to 4 different locations; VC, 2D Panel, Exterior, and Tower views. Thats 4. In XP9, they have a button for each of those, not a 4 way button. That alone is a big 'crevice' for FS pilots to deal with in going to XP9.
Setting up buttons in XP9 is a bit timely and crude compared with FS. FS is laid out much nicer in setting up buttons. XP9 looks a bit old world, though you can do a 1,000 things more with the settings in XP9. XP9 is an amazing and flexible sim, but can be difficult to new-commers. Very difficult. In fact, like I said, most just uninstall it and put it on the shelf instead of figuring out how things are set up.
Also, with ATC and AI traffic, and buildings on the airports, FS 'appears' to be more advanced and so others will think, why go backwards....
That is a in-a-nutshell on them, in a basic comparison.
I really like the sim, but my work is in FS and it cannot be converted to XP9, so I am stuck in FS, so I rarely get time to fly in XP9.
Also, I think XP9 looks far more realistic by way of ground terrain and sky and water and Autogen then FSX does. And..... It runs smoother with moderate settings, while FSX cannot run on 98% of the computers in the world at moderate settings.
But... FSX has things that XP9 does not have, and also, its easier to run as we have already learned FS...
Bill