Still haven't read it thoroughly, but I can make some general remarks.
This book is in general a mechanics-lite book. A lot of space is taken up with flavor text of Roman history, culture, gods and cosmology, customs, and peoples of the Empire. The book will be useful for applying Roman flavor to a campaign. It has some standard practical aids like a long list of Latin names. However, as I stated earlier, some people will be disappointed that so much space is being used for flavor text that is general history and accessable from an Encyclopedia.
One of the most useful flavor bits in the book from an RPG prespective is in the geography section. Each region has an 'Adventures in [place]' section, offering suggestions of what PCs could do in the area.
Thtat's not to say there isn't crunch. Details are given on Roman weapons, equipment, gods, and the cosmology. There are three new domains I believe, and a number of new spells. There are 5 PrCs.
Teh book does have a lot of suggestions on how to apply core D&D classes and races into a Roman campaign. If you want to play a Paladin, the book suggests where they might come from. The core PrCs have suggestions. Even Demi-human races are mentioned. Also, the'es a list of Core monsters which can be used in a Roman campaing.
Overall, this book doesn't do anything very drastic. It's standard D&D in ancient Rome. Other than some brief suggestions, there's no major changes to the D&D rules to fit them in a ROman setting. DMs who want to preserve an authentic Roman feel to their campaign will have to do some of their own work if they use this book.