This is going to be a short review because it's the sixth and final book in a very complex series and everyone who's reading this story is going to read it anyway.
Codex Alera is a military/fantasy series. It takes place in a world similar to earth, but could be someplace else entirely. It's got cities, but also farms and estates, called 'steadholts'. The people of this realm have the ability to use and attach 'furies' which give them specific talents such as manipulating wood, earth, water, metal.
It's a somewhat feudalistic world with the stronger 'crafters' having all the power over their countrymen.
The six books present the arc of what amounts to a world war. The fifth book was rather depressing, but this one, being the culmination of everything was big and powerful and exciting.
It just ended too abruptly. I've been reading reviews and almost to a one the ending was criticized as too short. There just isn't much denoument here and it's sorely missed.
But I couldn't even take away a star for that since scene after scene is masterfully put together.
A lot of Butcher fans don't love this series because it's really about one never-ending war. All relationship building takes place with that same war as a backdrop and in that context. It's battle after battle, too. But there are still bold hints of Harry Dresden in Tavi -- the main protagonist -- and Butchers humor remains intact.
It's a good ending even if I sincerely hope he'll give us a little something more to settle some of the dust he kicked up in this finale. Not sure what he'd give us exactly, but there are a lot of loose ends that need exploring.
ETA: why is it my 'short' reviews always end up as long as my other reviews? LOL.