I just started watching last fall, after refusing to watch the entire time I lived with my roommates because, well, I couldn't see how a show about killing zombies could possibly be entertaining and every episode I saw them watching was stupid.
Besides, that part in the first few minutes of the first episode where that little girl turns out to be a zombie and Rick shoots her in the head got me too upset to finish watching the episode. I've watched four seasons and it still bothers me to go back and see it.
What I ended up liking is that the show is about the community the survivors form way more than it is about the zombies. Like someone above mentioned, it's about how people change in a lawless world, how they adapt, how they define morality. In a lot of ways, it reminds me of Breaking Bad.
Season two was actually my favorite season. I hated it when they got to the prison, I was very glad when they left the prison (trying not to spoil). As for season 5, I think the jury is still out on it. Last weeks episode S5E03 was horrible IMO, but I had a migraine all day and into the night. I've liked the other two episodes this season so far.
Side note, the way they keep "rotting" the zombies, it won't be long before they all just fall apart on their own. What then? Will civilization flourish? I think that's my biggest question right now.
