RU.08 said:

The thing I don't like about this painting, isn't the rock, it's the left wall that is recessed behind the vertical "door" that just looks so fake because there's no depth to it (it doesn't look like the wall is going back behind the door). And also for consistency the right-hand wall should be coming further forward. I guess this is the problem when a painting is done "in-place" and there's no time to go back and do another one to fix those things...

Why does the wall on the left need to match the wall on the right? There's no need for symmetry there. Also, who said that was a door? I've always thought it was just a wall with a garage like door retracted underneath.
I don't see much problem with that part of the composite myself.