Forget what everyone is quibbling about with the mechanics and details of the apocalypse. It's science fiction. It's also not the point of the book.
I'm only at the episode titled Predators right now and the way that they resolved a conflict was way easier than it was in the book. That decision really set the whole stage for the community at that point. This was way too easy because the writers wrote it that way.
Responsibility and leadership are things Ish learns fairly early and after 17 years he's kind of like "I guess I'm the leader here" on the show.
These are reasons it's not a 5/5. If the people whining about the realism of the snakebite and such would put that away just like they should in most sci-fi they'd enjoy the story a lot more. It's not about "survival" as much as "is it even worth surviving, and does the earth even want us here".