Of all of Butcher's Harry Dresden novels I have read to date Summer Knight is by far the most enjoyable. Reducing the horror quotient of the previous book in the series, Grave Peril, and upping the insights into the workings of the worlds of magic and the 'faeries', the universe that Harry Dresden inhabits is becoming increasingly more rounded and interesting. Even the character himself is becoming more agreeable company. By the end of Grave Peril his world weary cynicism had been replaced by depression and sadness, and we find him is a similar state at the beginning of this story. During the course of Summer Knight however, he undergoes something of a change and by the end is back to his former, sarcastic, non-conformist wisecracking best.
I just hope that Jim Butcher maintains this standard with the next book. Having become a little disenchanted with the series post Grave Peril after Summer Knight I will once again be keen to find out.
Oh, and as always, word to the wise; if you're new to Harry Dresden buy Storm Front first and work through the series in order. The central stories of each book might work in isolation, but understanding what has gone before is important to the enjoyment of the books.