My curiosity got the best of me. Shame on me.
Make zombie movies care again.
"Train to Busan" borrows from the disaster movies of the 70s like Airport to quickly introduce the characters and make you care about them. Once the train got running the movie never stopped again. It made the most out of the setting and it's characters, even if they only had limited screen time. In the constraint of a horror movie, that dips it toes into the drama genre it worked perfectly. Only the convenience of the new rules on how the zombies could be fooled was a bit distracting, but otherwise it would have been a short movie.