I recently came across Writing Popular Fiction by Dean Koontz. I had never read anything by him and I just had a vague impression that he was a thriller writer, but it seems that he began as a science fiction writer. I read his entry on SF-Encyclopedia (in which they call him mainly a horror writer) and the following quote intrigued me. "The sensibility that would find horror congenial quickly revealed itself in a tendency to write stories in which, cruelly and effectively, the boundaries of human identity were stretched."

I'm not interested in reading horror in a SF setting ("not that there's anything wrong with that"), but I would read identity stretching SF that has horrific elements. Any opinions on Koontz's SF stuff from the late 1960s and early 1970s?