In my review of Water Born, I did not have any negative points to make, as I thought the author did a great job in everything he set out to do. In Black God, you still have the good qualities of Water Born. However, they are alloyed with some actual flaws (or what I considered flaws), which make Black God moderately less enjoyable than its predecessor.
On the positive side the author continues to build out the magic systems, myths, cultures, and history of his world. And this continues to be enjoyable; at many points it reminded me of Avatar in that by the end there is a complex dance of systems that have all been slowly introduced and built up. You also find out some neat secrets in the world-history and architecture, some of which made me laugh, other of which I found very clever. So, the good stuff from the first book is still there.
On the negative side, this book felt about 200 pages too long. Some of the character beats become repetitive, some of the reversals happen too often, and some of the danger of the first story seemed gone. A second major flaw was that to a certain extent, I did not care who actually won the climactic contest. The first book had a more focused ending, centered around whether the princess would live, die, or something else. That was fine, and it is carried by the fact that you actually care about the protagonist and don't want to see Princess-Hermione die. In the second book, the contest is about a much more abstract cause, and I could see good arguments for letting either of the factions win. It is a bit like if you had the Wheel of Time story, but rather than being a struggle between Good and Evil, it was a struggle between Lawful-Neutral and Chaotic-Neutral. The story and plot are still interesting and suspenseful, but the proposed conflict is less so.
So, my fundamental apathy about the ending combined with the extra 200 pages made this a much less taut of a read.