I watched the Branagh film on a recent flight.
It's... OK, I guess. I'd recommend anyone who wants to see it read the book first. The twist is preserved, but in the film doesn't work quite as well.
The basic problem (for those who are curious) is that the book takes you there through a couple iterations of Poirot interviewing the passengers, and showing exactly how he teases out each little piece of information that finally causes the truth to pop out at the end. The film, constrained by running-time concerns, can't do that, so several things that are separate and gradual revelations in the book are part of one big reveal.
A lot of the fun of the book (for me, at least) is the series of small shocks as he goes through the initial set of interviews and comes away with nothing, then figures out the pieces of the puzzle, confronts other people with them in later interviews, and explains how he worked them out from previous clues. That gives the eventual solution of the murder an entirely different feel.
There's also the usual amount of gratuitous deviation from the source in adding a bit of action and fiddling with characters, which also detracts a bit. The worst of it is that the moment when Poirot's solution is finally confirmed -- which is done in the book with a wonderful single sentence uttered by one passenger -- was changed entirely and became much more cruel than the book, in a way that deviates from how Christie usually presents Poirot's character.