It is, as they say, As Real As It Gets.

I used MS FS5 when I got my IFR endorsement, and was able to do it in the minimum hours needed, saving me at least a grand.

MS FS was the engine for some military sims in the early 2000's, and Qantas pilots did IFR currency practice on it when I was flying in NZ.

Although the terrain was pretty good, what made MS FS acceptable for pro use were the excellent instrument panels.

or X-Plane?

Having purchased X-Plane 11 while waiting for the new MSFS, and previously coming from an unmodded copy of FSX, I have never been more disappointed in a simulator product. I don't know how a system made with more than 10 years of extra effort can fall so far behind the competition. The terrain looks like garbage and doesn't make sense (Why did you generate a high voltage power line IN the road, you know exactly where both are!?) and the roads look amateur at best, the built in planes are mediocre and uninteresting, with half of them feeling nearly unimplemented at best, ATC that is completely unusable, and somehow worse performance, with a VR mode that feels not even quarter-assed. The minimum I can say for it is the interface seems okay and usable.

I guess it's not the market leader for a reason