In my comments on the first nine books I mentioned how the Dresden books follow a distinct formula, and how that formula becomes more apparent the more you read them. There is definitely a formula involved, but it is less obvious if you read the books with some interval of time between them. I read the first nine in a relatively short period of time, but read the tenth one about a year later, and as a result the formula was a lot less noticeable, and the read was a lot more enjoyable as a result.