My first exposure to Murder on the Orient Express came when I was ten years old and we were flying to England to live for the next five years. I stayed up until very late to watch the entire movie. I remember that the entire cast was brilliant, but I absolutely adored Lauren Bacall (I still do). This also was my first introduction to the work of Agatha Christie. When we landed in England, we stayed in Harrogate, not far from the Swan Hotel, where Christie's fugue state landed her decades before.
Since that day, many years ago, I have read and re-read Murder on the Orient Express. I still cannot read it without picturing Lauren Bacall and Mrs. Hubbard. This does not detract from my enjoyment of the novel.
Agatha Christie was the first to admit that she was not a great writer; she was a good writer. What made her great was her ability to study, understand and portray the human condition. Her character are wonderfully flawed; her portrayals of them, wonderful, but not the least bit flawed.