What is his best film?
The Tingler (1959) would be my pick.
shareOf those I've seen it would have to be House on Haunted Hill, one of my favourite Halloween watches (and the only Castle flick that I own). Homicidal is a cracker, too.
shareI'd have to look at a list, but that's a pretty good one.
Edit: Does Rosemary's Baby count as a Castle film? He only produced. He wanted to direct, but Robert Evans wanted Polanski.