This is the first book to spin off of the Castle TV show and I recommend to read it first (not something I did) as the second books' tone will make more sense.
In any case - I enjoyed the book for the same reasons that I enjoyed Naked Heat; you have the "character"of Richard Castle writing a fiction based on the characters in the TV show. Confused? Don't be just start watching Castle on Monday nights - you can jump right in the show at any point.
I just wish I knew who is the ghost writer for the series - it's a lot of fun.
Next up - Non-Fiction. Yikes!