This is a great piece of kit. I need to get something similar for my own Zanzibaris.
As for the rocks, I think the issue might be less of the overall finish of the rocks, but rather the fact that they look to be a rather "cold" grey as compared to the "warm" browns of the fort. The foliage in the last pic looks very effective, and maybe it would suffice to shade down just the spots where the rocks meet the fort, to give it some more differenciation. Maybe mix some "chocolate brown" and some anthracite grey with a spot of pure black, water it down a bit, and define the edge with a good, fine brush.
But that may be a nitpick. I think it's absolutely fine as a gaming piece, yet could benefit from some careful, gentle additions, so as not to overdo and ruin it.