The first book was a mixed bag, very weird pacing, but the world-building got me. The second book gave a new unexpected perspective on everything. Third book, another new unexpected perspective. Great demon-killing action all the while.

At the fourth book there was unexpectedly no new unexpected perspective. At this point I am interested in nothing but learning the answers the the existing burning questions. What's in the Core? What happened in the distant past? The big secrets. Instead we get weird politics, new characters I was absolutely not wishing for, and maybe 10 pages of progress in the main plot.

Bad omen, but it's not like I will stop reading a 5-volume series after the 4th volume. So how did the 5th and last volume do?

We got absolutely no big answers. What's in the Core? Magic! What happened in the past? A tunnel collapsed and Kaji kinda forgot about his crusade. What was the point of Rojer's character? Nothing.

The plot at least comes to an end. But even that I found unsatisfying. Arlen sacrafices himself to the Core and casts a spell that kills all demons. They could have done it as soon as he learned misting! Okay, maybe he needed to build up his control and willpower. But there was definitely no need for capturing Alagai Ka, finding the Spear of Ala, battling the Queen, etc. His ultimate spell made all the efforts of the rest of the cast pointless.

A new demon-fighting mechanic is added, but it is also less interesting than in previous books. They can now simply ward the air. In other words cast spells like a normal wizard.

Despite all my complaints, the book still has a unique atmosphere. Very uniquely all bodily fluids are featured at some point. Make a list of fluids you can think of with boxes that you can check as you read. See if you were able to list them all in advance!

Half the cast being pregnant is really unique too.

As a 5th book it's also inevitable that you have a close relationship with the characters by now. I enjoyed the bits of fun the author has with them. The large amount of history also means a lot of baggage. No two characters can meet at this point without each of them having done something good or (more likely) bad to a relative of the other in the past. Recalling these events is rote, but also necessary unless you kept notes while reading the earlier books.

I'd recommend reading maybe the first three books and no longer!