The Good: The book is short, and at 178 pages, it actually feels a lot closer to horror than any of the other books (I've always been a big believer that, Stephen King aside, short stories are the best medium for horror). The book has barely any Bella at all, although she is described as sweet, amazing and special a lot in the one brief interaction Bree has with her. Finally the vampires actually act like vampires, killing people and having serious hunger issues, making them the closest thing I've seen in the entire saga to vampires as I know them.
The Bad: Like Bella, Bree falls in deep teenaged love with a boy about 10 seconds after she meets him. Also the giant fight sequences I missed in Eclipse is also missed in this book. To be fair to the author, writing fight scenes is not her strong suit, so this might be a good thing. Finally there are a number of continuity issues, things that don't match up with the stated events of the novels, which comes across as a little lazy on the part of the editors of the book.
Overall this book is tricky - if you want to read great vampire fiction, this isn't it, but at the same time it is leaps and bounds above the rest of the series from a horror point of view. Unfortunately as it is a fill-in-the-gaps-type story, you really need to read the other books to figure out what is going here, so there you have it.
Next I'll look at the series as a whole and then the soundtrack to New Moon.