I read almost all of his books, not all are that grim. Some have a humorous touch, at least on the surface, like Ubik or the book from which "Total Recall" was made, but I agree on your well-put overall conclusion about his type of genius!
Definitely humor. Despite his darkness, he was a kind soul I think. That comes through. As I read more of his books (going through Ubik now), I also think he is more relatable to a male audience. I say that with regret, because I appreciate him so much, but he does not seem to be able to extend his POV to women. I don't think that would be obvious to a male reader, but it strikes me (as woman). Doesn't detract from the value of his book--that is so far above something as specific as gender. Still, it is there and rather inescapable.