Not so great Gladys?
In style I would say she is nearer to Margery Allingham than to Christie, Sayers, or Ngaio Marsh. There is an odd other-worldliness to her novels (at least judging from Tom Brown's Body, the first I've read). Mrs. Bradley, professional psychiatrist, researcher into the supernatural, and amateur sleuth, investigates when she happens to be in the wrong place at the right time. All is not well at a boys' boarding school, when an unpopular master is murdered in very strange circumstances.
To be honest, this really didn't grab me. It was an interesting comparison read to other crime novels of the same period, but it just didn't draw me into it - although quite why not when it had a quirky cast, a pseudo-Roman bath, and a dollop of witchcraft, I don't know. Perhaps it was because I found the characters largely unbelievable, especially Mrs. Bradley - I'm afraid I didn't warm to her. While Mitchell seemed quite happy to break the rules of detective fiction whenever she felt like it. A particular bete-noire of mine.
It was entertaining, it certainly wasn't the worst detective novel I've ever read, but "Great?" Perhaps I just got the wrong book....