Long and run on, or acceptable?

Writing a book I am using the following sentence "Their eyes met for one final glance as the old man’s naked form went limp and lifeless, the blade still protruding from his skull, intensifying, deforming and twisting his lifeless smile into a grim visage."

My proofreader says the sentence is too long and incorrect, but did not give me any advice on how to improve it. Is it acceptable, or should I try to shorten it?

Thanks!