It had a really intersting storyline and was completely diferent from all the dramas I had ever seen.
The caracters had flaws and virtues and, on top of that, were experiencing the apocalipse. The problem here is that the monsters and special effects aren't what makes us scared. What really messes with our heads is that we get the actions they are forced to do and agree that we would do the same, no matter how vicious they seemed.
The only reason I gave it a low-ish rewatch value was because of how recently I had seen it. Totally worth it, though!