On a technical and narrative level, excellent writing — this novel is compelling on multiple levels. Greene comes to paint all his characters as archetypes, even stereotypes, but continuously pokes at these types, showing that even those bound by their “nature” or society’s rules/conditioning have moments of human chaos and nuance, never fully remaining one thing or the other. 

The story itself is also not quite a mystery, but you can never fully see what’s coming around the corner, either, which certainly kept me engaged. 

Ultimately, though, the book is anti-Semitic in Greene’s perpetuation of certain stereotypes and tropes, even as he criticizes overt violence against Jewish people. Would not recommend other people reading this book without significant critical distance. 

I really love Graham Greene but haven't read him in a while, and this probably wasn't the best book to get back into his work. It's an early one, 8 years before The Power and the Glory, nearly a quarter century before The Quiet American, and I found it unsatisfying. I never fully bought into the characters; admittedly, it's hard to flesh them out when the story is set on a single train ride, although adding in substantial backstory set elsewhere for more of the characters would have helped. That might have helped a great deal, but of course this would have made it a different novel that was perhaps less focused on the train ride itself. 
Published in 1932, the casual antisemitism of nearly all the characters was difficult both to understand and appreciate as a part of the story. Was this really what the world was like? I'd like to hope not, but it tended to make the characters a little less believable: I was constantly wondering about characters like, "Wait, you really find this person revolting because he's Jewish?" And the internalized antisemitism—the shame—of the Jewish characters was uncomfortable to read. Now, I don't believe books need to be (or really, should be) safe spaces where a reader is protected from all discomfort, but what I'm trying to explain is that the ongoing, casual, sustained antisemitism assumed by all the characters actually made the story a bit less believable for me. (Now, going back and reading the introduction after finishing made it clear that a lot has been written about this subject in the novel, so I'm fully aware I'm oversimplifying the issue. I'm not trying to make a literary case about Greene's intentions or anything, I'm just pointing out the effect of this theme on me as a reader of this piece of literature. YMMV as always!)