Me too, but then I quite like most of the early thriller/far fetched ones in a totally different way to the straight detective stories - The Secret Adversary, Why Didn't They Ask Evans, The Secret of Chimneys (which is bonkers but deeply enjoyable) and The Seven Dials Mystery.
Not a huge fan of Partners in Crime but I do like N or M. Though no wonder Tommy is a bit slow, the number of times he's been knocked on the head...
Five Little Pigs, Sad Cypress and Crooked House are all excellent reads. I want to like The Hollow but the Angkatells are all so totally unlikeable.
Good point earlier about the much-used plot point of 'everyone looks different in different clothes' - Lord Edgeware Dies, After The Funeral, Murder in Mesopotamia, Evil Under The Sun, The Secret of Chimneys, The Mystery of the Blue Train...
And then there are the 'nicked the identity of someone the rest had never met' books like Hercule Poirot's Christmas, A Murder Is Announced, Dead Man's Folly, Taken At The Flood, Mrs McGinty's Dead, Cat Among The Pigeons, and a dozen others.
Just remembered that I really, really don't like Taken At The Flood.