I thought the Spiral was a quick and easy book to read. The main character Erma is a researcher who's mind is always racing, trying to work things out, and that is reflected in the writing style of the book. It is lots of short sentences and quick paragraphs that means you just fly through it.
That isn't to say that it isn't a good read however, it's pretty dark in places and takes a pretty unexpected turn. The main character isn't the most likeable in the world, she is deeply deeply flawed so it makes for an interesting dynamic between you and the characters, which is a key theme in the book. It is steeped in nostalgia for choose your own adventure books which I remember growing up with, I used to love them, so I kept hoping there would be an element of it included and I wasn't disappointed, there is a section in there and it was a really nice touch.