The crime is set in a nondescript English village - much the same setting as Agatha Christie picked for Murder is easy. So there's none of the great background set-up that you normally get with Dorothy L. Sayers. It is very much to the point. But although it might not be a typical Sayers, it is an extraordinarily good crime thriller.
It does suffer from some of the less desirable aspects of the 1930's. There is a certain level of racism, but to be fair to Sayers, she doesn't condone this, and indeed Wimsey goes out of his way to proclaim the innocence of a black man, who is in the process of being framed for murder largely because the murderer thinks that his colour will make him an easy target. A repulsive thought but only too true at the time, and, I suspect something that still happens even in our rather more enlightened times.
So what's good about it? There's a great murderer - coldly brutal, and written incredibly well. There's also a brilliant murder method - which really made me sit up and think - I wonder if that's been used often in reality? It's amazingly simple, and appears to be virtually undetectable. Not the greatest of the Lord Peter Wimsey mysteries, it lacks the extras that turn them from your average crime story to true novel status, but as an object lesson in how to write a great crime story, they don't come much better than Unnatural death.