Well, he was a SF writer. And fantasy. And horror. Not that there is anything wrong with that.
Based on the videos I've seen of him, he had to be one of the most egocentric writers of the last century. I was not surprised at all to see he had five marriages. I'm glad the last one lasted. Sorry to see he went through a lot of pain physically and emotionally his last years. I don't like to see that happen to anyone.
But I will always hold him in fairly high regard for his Star Trek episode City on the Edge of Forever and for his short story collection Deathbird Stories.
I wrote that because he introduces his first video by saying:
“I'm a writer. Call me a science fiction writer, I’ll come to your house and I’ll nail your pet’s head to a coffee table. I’ll hit you so hard your ancestors will die. I’ll punch you so hard your grandmother will bleed. I’m a writer. There’s no adjective in front of it. I’m just a writer.”