This is the one where The Dresden Files really came into its own. Everything about this book works. Harry's guilt complex after losing Susan is well-handled, the Alphas make a welcome return, Murphy finally gets back into the action, we finally find out who Elaine is, we learn how faery politics work, and we get two of the greatest battle-cries ever. It takes Harry a long time to make progress on the investigation, but that actually works to the book's benefit, and allows a lot of the book to run on the problems he encounters while investigating, and slowly revealing the true scope of what's going on. The truth is, the plot is actually fairly simple, but the complications form simply because Harry expects them. The final battle is the biggest the series has done so far, and the scale of it is incredible. It really makes everything leading up to the finale pay off, and it's a heck of a lot of fun. Summer Knight is the book where Jim Butcher
finally manages to make everything fit, and from here, The Dresden Files begin to be one of the most awesome series ever.