I was floored by this. Possibly the best TV movie I've ever seen. Though many elements of the story are unique to this interpretation, everything that is new is so good that I'm not in any big rush to watch any of the other adaptations (or to even read the original book for that matter).
I went into this pretty bare, having only seen a few early series episodes of the Poirot TV show. That small experience helped to elevate this, given the stark contrast in tone between the early era of the show and the much more bleak, dramatic tone the later series takes. Seeing how Poirot is just tired, and completely done with everything made this so much more emotional.
The performances here are incredible, the writing is incredible, the score is incredible.
My singular complaint is some weak CG shots of the train, which the film easily could have done without entirely. Regardless, this is one of my all time favorite movies. Poirot is so heartbreaking, how he wrestles with his morals and religious faith, DAMN now I gotta go watch it for the 4th time this year!