This show is extremely binge-able, I saw the first season in 3 days. Every episode has a thrilling scene and usually an amazing cliffhanger that just forces you to hit start on the next episode. It is not a typical zombie movie.
The cast pull off their roles beautifully. There are a lot of characters, yet despite this, you remain interested in all of them, regardless of which character the camera follows. It is incredibly interesting how the film follows so many different characters during the situation. All the necessary characters who needed a backstory or insight into their family life got one, and it made so many scenes heart-gripping and impactful. Even those who we don't know much of their background had such unique personalities. As the series continues, the unlikely bonds between many of the characters, as well as the blossoming romance between a few of them, adds to the series.
There are many other aspects that make this series amazing. The gore, the intensity of the scenes, the unique ways the students traverse the school and stay alive, the concept of the infected but asymptomatic 'half-bies...' But for me, the characters are really what makes it amazing.