Murder on the Orient Express isn't my favorite Agatha Christie novel (that would be The Mysterious Affair at Styles), but it does seem to be the most frequently adapted into film. It's been a long time since I've seen the 1974 movie, but I do remember enjoying it a great deal; and now that I've just seen the new Kenneth Branagh version, I have to gush. This movie was good. Damned good. It was a hell of a lot more faithful than the Poirot episode from 2010. (That series never failed to take annoying liberties with its adaptations). Good screenplay, excellent music, plenty of fun little Easter eggs for Christie fans to notice, beautiful cinematography, and it's fun to see the all-star cast playing off each other (with Branagh and Pfeiffer being the highlights).
I have to admit that going into this film, I was skeptical about Branagh playing Poirot. After all, David Suchet has owned the role for so long, it's hard to imagine anyone else doing it justice. But he pulls it off: his Poirot is at once more active and more contemplative than Suchet's, but still quirky and humorous. If I have one complaint (other than the extra-wacky mustache), it would be that Branagh's Poirot is portrayed as not just methodical, observant, and exceedingly fussy (as he is in the novels), but downright obsessive-compulsive. The "OCD detective" is a cliché nowadays (mostly thanks to Adrian Monk), instantly recognizable to aduiences; and in this movie, it serves to make Poirot more likable (his particularities are a compulsion rather than just dickishness), so I can see why it was done this way. But it's not exactly who Poirot should be.
What the movie does get right is Poirot's moral code, and the way this particular mystery and its solution wind up challenging that. The screenplay for this move takes it one step further, delving into Poirot's beliefs about what it takes to make a human being take another life—what turns a person into a "killer". There are moments when Orient Express makes you sit up and think—exactly the opposite of the super-hero popcorn flick that rules the cinema these days. That isn't intended to put down super-hero movies, which definitely have their place; but I didn't know how much I needed to watch a good, well-paced mystery movie until I saw this one.