Armies of By Fire and Sword volume 1 does not have a theme like the previus expansion, "Deluge", but instead offers a mix of new skirmish lists, division lists and historical commanders for all nations.
A number of these new lists have been available as PDF's though I know that not all of them have been available in English - such as the Gdansk and Courland army lists to mention but a few. They have however been overhauled or tweaked for this printed release. For example the Gdansk list has been split into two skirmish forces, offering one offensive and one defensive list which once again makes this army a viable option for tournament play but additions have been made for the divisional level adding a regiment of Dutch infantry among other things.
What the book offers in great quantity are lists that provide something completely new, different or at the very least interesting.
We get a skirmish list for the Cossacks that is pretty much all cavalry!
We get Polish levy of nobility lists that come in variants in between themselves and that can be themed even further by adding one of six historical volunteer/levy commanders to lead them!
The cavalry oriented Poles receive a skirmish force based around infantry and pikemen!
There is a Polish highlander skirmish list that offers you vast amounts of peasant/robber quality troops with some interesting special rules and the option to field improvised wooden cannons. This list
Several lists that mix nations, such as Cossack-Tartar skirmish lists, Polish-Transylvanian and Ottoman-Tartar.
There is an ottoman garrison list that allow you to field Janissary infantry at skirmish level.
The Muscovites receive some much needed additional skirmish forces allowing you to field reliable boyar sons backed by reiters and a list that offers a mix of streltsy/border dragoons/don cossacks!
At division level you get a bunch of historical divisions that offer some very interesting options. Some of these have also been published as PDF's before but there are a lot of new ones.
Among the lists that stand out the most imo is the Polish division led by king Jan Sobieski, offering you a powerful cavalry regiment filled with winged hussars - backed up by many small regular infantry/dragoon formations and hordes of peasant rabble.
Or how about Cossacks backed up by Transylvanian regiments? Or a historical Swedish division composed of almost only National Infantry regiments!
There is also a variant division called Allied Vanguard, that mixes Swedish Brandenburg and Transylvanian regiments - it comes in 3 different variants each with its own historical commander and special rules.
And finally the characters, that can be added at a divisional level. The Ottomans get a Cavus (envoy officer) to help command artillery, or friendly regiments as an additional commander. The cossacks get a camp master which basically allows you one more commander that focuses on your war wagons and the Polish-Lithuanian commonwealth gets 6 partisan/volunteer commanders that can be used with various Partisan/Levy of Nobility skirmish forces to make them more unique and add some interesting features ranging from increasing morale stats of certain units to adding Reconnaissance effects to your force.
At first glance the book may look on the thin side and not very focused (compared to Deluge), one may miss a theme. But if you give the lists a good read you will discover that a lot of flavor has been added to all nations available - I think the new lists will make coming tournaments less predictable since many armies now have "counter lists" and are less prone to suffer from being boxed into a single role.
I hope that players will give the new divisions a try, the game is great at this level even though most people tend to focus on skirmish battles. The new divisions, with their historical commanders and lots of special rules will make for great campaign games but also fun standalone battles where both players pick forces from the same period to keep things a bit more in line with history.
The book does not include any "rules segment" as such, it is completely focuses on adding army lists. It does however introduce a bunch of new special rules for certain units and commanders.
The quality of the book itself is excellent, the binding is just as good as in Deluge. Cover has a good matt finish, illustrations are great and presentation is top notch.
If I have to nitpick then I would say that the Index, while decent would be even better if it included subcategories with each nation, and I would probably have preferred to have all skirmish and division and characters of each nation bundled together rather than spread out on skirmish and division level segments but I understand the idea behind the way it has been done.
All in all a good buy if you play By Fire & Sword, chances are you will find more than one list/addition to your liking to warrant a purchase - maybe even tempt you into buying a new force or expand your current one with units from another nation.