It's not an fsx killer - but it does have some awsome qualities.
It's extremely flexible, and its flight dynamics are insanely good. For example, including with it is one of 'Austins designs', a FORWARD sweep, flying wing, engines attached to the end of the wings. The amazing thing is, the second you turn OFF the simulated fly-by-wire, the aircraft will go completely out of control.... and the fly-by-wire actually works by moving the flight controls, it doesn't magically change the flight dynamics.
You can also go in the X-15 and attempt to break speed and altitude records. It's interesting, once you get above the atmosphere there's no gravity and you have to rely on the hydrazine thrusters to change which way you're pointing!
And you can fly on mars.
And I don't think it's possible for a X-plane to even come close to MSFS in terms of graphics, gauges, or screenshots - so if you're after a heavy simulator X-plane is not going to give it to you.
http://www.x-plane.com/