The reviews on the cover of this book say that the author is:
"One of fantasy's premier voices."
"Parker's way with words can be as beautiful as it is technical."
"Parker's skillful control of pacing, expert rendering of characters, and subtle sense of humor add depth and believability."
Note that none of these reviews said that "the book is enjoyable to read", or "I liked any of the characters", or "there was some discernible plot or other reason for this 500 page book to exist". So. This book is set in an alternate version of the Byzantine empire, where the two halves of the empire have been fighting a civil war for the last 90 years. Notable features include two brothers who are genius commanders and are on opposite sides of the war, a Masonic secret society that is spread through both halves of the empire, and large tracts of devastated and depopulated land. The primary problem with the book is that it never gives us a reason we should care about the events in the book. The two sides of the empire seem approximately the same, and approximately evenly matched. There isn't any grand threat, or quest, or important sequence of events going on. There are PoV characters on both sides, and none of them really stand out enough that you would root for them, and none of them get quite enough screen time that you become attached to them. There aren't any idealists, or any particularly charming rogues, or any real villains. The best it can claim is some mildly interesting characters, going about doing dangerous and mostly useless things in a cruddy war zone. Admittedly, by the end of the book you can kind of see where the plot is starting to go, and what the next 2000 (!) pages of this series are going to be about, but man do you not care by that point. If it takes 500 pages to give the reader a hint of why they should care about the novel, something has gone terribly, terribly wrong.
Another problem with the book is that it is a book about medieval warfare but it does not get medieval warfare right (at least to the best of my understanding). For instance, the first ~5 pages of the book are about a battle, and none of it makes sense. One side out numbers the other 3 to 1, and they are on a flat field, and yet somehow the larger army is "pinned down." ??? Another crucial factor in this battle is that the smaller army doesn't have arrows for its archers, so it looks like they will have to retreat because of that. This isn't really right; archers weren't a decisive factor in medieval battles, and it would be entirely possible to fight without them. Archers could be useful, they could harass and disrupt, and if given enough time they could destroy a force over the course of days, but they simply would not play a large role in the brief and brutal clash of melee. So the clever trick the genius general uses to solve this problem is to send his heavy infantry out with siege structures behind them, so that the enemy archers will shoot at his infantry and the misses would hit the siege structures, which could then be withdrawn, and then the arrows stuck in the siege structure could be harvested and reused. And this is terrible for many reasons. 1) is that this is stolen directly from the Romance of the Three Kingdoms, except for in Romance it was with boats and it was in the fog and it at least a little made sense. 2) there wouldn't be any time for any of this. You don't get to wheel forward infantry and engines, have them shot at, wheel back the siege engines, harvest the arrows, etc. It would all be essentially over in 15 minutes as the larger force just marches forward and swords everyone. 3) The genius general says that "yes, we don't need the heavy infantry but we do need arrows" which is just crazy talk, it's like saying you don't need tanks but you do need nerf footballs. Well trained men in heavy armor were fucking terrifying back then and could put down basically any number of lighter conscript forces. Anyway! This nonsense continues through every battle scene in the book. There's this consistent idea in the book that battles were these precise chess games that were won by genius ploys, rather than brutal and confused scrums that were usually won for reasons like "That side had 5 times as many guys on the field." There's also this consistent, modern understanding of battle that "ranged weapons are really powerful and deadly." Which really wasn't true until around 1850 or so. And this is doubly weird, since the author is famous for his book _The Walled Orchard_ about an army which is (Spoiler!) beaten by ranged weaponry, but it takes like a full week for the process to actually occur and for ancient ranged weapons to inflict enough damage to shatter the army.
Anyway, I could go on with the other problems that I had with this book. But to wrap up, this series seems more like a make work project for the author than anything that would be interesting or gripping to a reader. The author needs an editor, he needs to get to the point, and he needs to give the reader a reason to care about his story.