In short: Carnival of Souls by Melissa Marr has a ton of potential, but is unfortunately bogged down with an exposition-heavy story that lacks in action and character development. 
 Creating dark and gritty fantasy worlds is something that Melissa Marr excels at. Her books tend to have these really sinister atmospheres that make for edgy and dangerous stories. And Carnival of Souls is no exception. Enter the world of the carnival in which cage fighting matches and masked seduction occur in equal parts. Transitioning between two different worlds - the normal human world and the parallel daimon realm - and four different characters perspectives, Carnival of Souls has a lot going on and a lot of potential. 
 Unfortunately, I didn't feel like the concept and premise of Carnival of Souls was used to its full potential. What should've been a dangerous and exciting read was more often slow and boring. I blame the crux of this problem on the poor world building. Melissa Marr has created a wonderfully complex world, but it is the execution of the set-up of this world that was lacking: a good majority of Carnival of Souls is exposition. The particulars of the daimon realm and the caste system are described at length and it really bogs down the story as there is very little actual action going on. The exposition-heavy story really hurts the pacing and reads more like a textbook at times as it is not integrated very well into the text. 
 And I can't say I particularly cared for any of the characters either. We never truly get to know any of them that well and that makes it difficult to relate to them. The romances were similarly underdeveloped and one of them was another ubiquitous case of insta-love. I spent Carnival of Souls feeling removed from the story and the superficial characters, not really caring what happens and eager to set it aside so that I could start something more engaging. And I hated the ending. 
 I can't help but think that most of the problems I had with Carnival of Souls could be fixed if only it was longer in page length. Very talented authors can get a lot done in very few pages, but I think even the most talented author would have had a hard time setting up such a complex world and still having time for character development and action scenes in just 300 pages. But as it is, Carnival of Souls was 300 pages of exposition - the execution of which was fairly poor and boring - and that's a shame because it really could've been a truly exciting story.