The only suggestion I can make is that the lighting under the rim of the top mushroom head looks a bit dark. In the films, it was bright enough to illuminate the dark ribbing in the trench beside it. I think you should probably texture a subtle glow into eaiter side of the trench, not too much, just enough to show the light spill.
Really, I can offer no other suggestions, such is the PERFECTION of this work of art. WELL DONE!