The Fire Sermon has a slower pace than most dystopian/post-apocalyptic stories, in my opinion, but that's not necessarily a bad thing- and that's coming from someone who needs quick paced reads. This one is actually more character-driven than plot-driven.
I liked Cass, Kip, and the other characters they meet up with eventually. I think I actually liked Kip more than Cass, though. The story is from Cass' POV, but while she starts out as a determined young child, somewhere along the journey (which is decidedly long and hellacious) she gets defeatist and that irked me a little. It made the third quarter of the book seem hella long. I do think it could use some editing down, but this is a review of an advanced reader's copy so that might already be in the works. I think Cass and Kip balance each other out a lot though, which is good. Plus, Kip can be witty, which I like in a person/book character.
I did get surprised at a revelation and some of the events at the end, which is always appreciated in a story. In a way I feel like I should've seen it coming because I am forever figuring out these things way too early in a book. I was happy I did not this time! Makes it more enjoyable not to figure it out ahead of time.
I recommend giving The Fire Sermon a try if you enjoy this genre. It is nice not to have a completely tired and worn-out storyline, but something unusual and creative.