There is something truly epic about the series. One of the characters, Small Sam, refers to The Lord of the Rings multiple times. There are some similarities, but I am more reminded of Game of Thrones. You need to be patient when reading a series like this. Small Sam appears in the first book and then doesn't pop up again until the fourth. There are so many characters to track and Higson clearly had the whole series mapped out before beginning, as the story loops back in time occasionally and you see scenes from new perspectives. It's brilliant and I love how it will challenge the reading skills of young people.
I'm going to ask our school librarian to add the whole series to her shopping list. Once hooked, I can picture students reading them the way I did: gulping them down, not coming up for air, and loving every minute.