Murder on the Orient Express is certainly a decent "whodunnit", although at this point the conclusion of the story is so well-known that I can't really judge how well it was executed from the viewpoint of a reader without that prior knowledge. It's a quick, fluent read once you get used to Christie's vocabulary and style of writing, which is (unsurprisingly) rather antiquated in some passages. I was a little surprised at the untranslated French interjections and phrases; people who don't know at least a little French might stumble upon them.

All in all I found it to be a great book to read for fun in 2 days. Some of the details and the general way the pieces of the puzzle fit together ended up being pretty satisfying and less one-dimensional than I remembered from whatever movie adaptation I watched ages ago.