Of course, as is Erickson's wont, there are new characters (most of them introduced in the prologue, but not all).
This is a very catastrophic book. Just like at the end of Book 3. But this one follows that suit throughout. There are major battles that don't turn out so well, and trustful alliances gone awry. The latter, once you get to Seven Cities. Also, the use of propoganda shows its ugly side near the end.
Just about all the characters from Book 4 are back (Karsa, Kalam and QB, Fiddler, Heboric, Cutter, Pearl, etc...). Also, there are Ganoes Paran, Trull Sengar and his Imass friends, and of course, Icarium and Mappo (not just a two second appearance, like in Book 4). Also, this is the book that Shadowthrone is most active in. Something that you've been waiting for one of these characters to do since the beginning of the series finally happens.
As always, there are insights on human nature, and the tendency for war. But in this one, the bulk of these insights are towards the use of the concepts of gods, and what they drive people to do (with many similar tales to things like the crusades).
And finally, there's the one thing that fantasy novels should never go without. A socially conversable demon that also likes to eat people's brains.