Train to Busan

Not only is Train to Busan a perfect zombie movie, but it's also a perfect film, in general. It hits the emotional beats just right, action scenes are beautifully directed, and there are tons of good ideas. The tension really works because you care for all the characters, you want to see them succeed. I genuinely can't think of anything wrong with the movie, it's just that good. If you've got the time, watching this should be your first priority.