oldmanhonah-
Agatha Christie wrote her books in different styles.
I’ll mention that right-and-wrong play a part in the above three books, as well as pure detection.
Personally I liked the Poirot books.
You may want to consider Ellery Queen books (if you can get them) – the full-length novels, not the short-story anthologies.
The Nero Wolfe series by Rex Stout is also quite good, and OK as far as I remember.