The book picks up right where the previous one left. I have an impression the only reason for the split of the story between books 5 and 6 was the author's desire to put a prologue with a nice epigraph at a certain point - this and the consideration of length of the resulting books.
The big bad enemy suffered a temporary setback, but was not beaten by any means. At least this gave the good guys time to regroup and collect their forces. For a lot of High Lords incoming complete devastation is not a reason good enough to stop their scheming, so for them it is business as usual.
At this point I will stop talking about the book which was exactly what one would expect from a book of this series and will talk about the series as a whole. Is it worth reading? It depends on what you want to read at the moment. Are you in the mood for some deep philosophical ideas combined with excellent character development? Look elsewhere. Do you want to read something similar to Dresden Files? Run away from here as fast as you can. Do you want a great mindless entertainment which I keep comparing to a summer blockbuster movie? Step this way please.
I mentioned minimal character development. It is still there for the most of the main characters. Tavi starts as a stereotypical Gary Stu, but he does develop some shades of gray as the series progresses. There was only one character whose development was very disappointing. The character in question had a potential to become as great as Severus Snape from Harry Potter whom I consider to be the most complex character in the children literature.
Alas, the person in question from this series takes an easy path of becoming a typical villain.
Speaking of characters, there was one other one who came out pretty much unbelievable, but for the rest of them they all served their purposes just fine.
Considering the fact that I gave every book of the series - including this one - 4 stars, this is also my rating for the whole. If you are looking for great entertaining story which will not put too much strain on your brain (and let us fact it, we all need to read such story once in a while) read this. As an additional bonus you will get a pretty good idea on the tactics of Roman Legions and why it was very successful at the height of Roman Empire.
In the conclusion I would like to commit an act of ultimate blasphemy and say that I like this series much more than Dresden Files.