The problem is that it's a global simulator: this is a major part of its appeal and marketing. If you only ever plan to fly airliners between handcrafted payware cities, it will look pretty great. As soon as you start flying VFR outside those points, the generated terrain shows its limits. I don't fly it often, but when last I flew:
* The generator couldn't handle windmills. You would see them as flat, projected images on the landscape with no 3d asset.
* It can't handle boats. Again, they're rendered as flat images on the water. Marinas in particular look bad, because they fade out as they get away from shore.
* It can't handle washes. You'll fly over the desert and see a glossy sheen of reflective water where the sim thinks there should be a waterway, but it's quite obvious that no water was present when photos were taken.
* It can't handle meandering streams. You'll see that same glossy sheen cutting a straight line over the terrain, while the photographed stream meanders back and forth.
* It can't handle bridges: you'll see cars drive right through the bridge and along the terrain underneath it.