Okay, so I'm a shameless fanboy. This book consists of the shooting script for the movie Serenity packaged with an extended interview with Joss Whedon and some pre-production documents also written by Whedon. Oh and a whole bunch of pictures from the movie and the production process. It's probably exactly the same stuff that's going to show up as extras on the DVD when that comes out in a few weeks. But when I saw it in the book store my brain went "Shiny!" and handed over the bucks.
On first watching we were pretty disappointed in the movie. We were in the process of watching the series DVDs for the third or fourth time and so we were completely steeped in the characters and the worlds as they were in the show. They changed for the movie in subtle but important ways and to us it was just wrong. After we saw the movie a couple more times the new slant became more tolerable and we could accept the movie on its own terms.
Reading the script makes it clear that the changes were definitely engineered in by Whedon and weren't a strange byproduct of the production process. There is stuff in the script that was cut from the theatrical release too so we're hoping there will be some deleted scenes on the DVD. Inara in particular got cut pretty heavily.
The pre-production memos from Whedon trying to give the production crew a sense of the Firefly universe are fun to read for Joss's self-deprecating yet goofily pompous tone.
It's a nicely put together little book of fan goodies.