That said, every book is a solid stand-alone story. No story requires reading more than the book it is in.

Yeah, I will mention that at the time I started reading them, availability of the series in the US was pretty spotty so I read a lot of the books out of order. I didn't find it impacted my enjoyment. Some of the later books have more continuity, particularly the later watch books, but I think the majority of them could be read in any order without too much problem.