This book held my interest until the end, but I wish the ending had come sooner. There are so many unnecessary words here. Probably a third of the book could be dropped without losing any actual meaning or even getting rid of any scenes, and it was sometimes a struggle to read through the extra stuff. 
 It was a very dark world in the metro, which I enjoyed. The cover of my copy says it's 'terrifying,' though, and it was not. A few places were creepy, but nothing else. Frankly that's good for me, because I don't like scary books. So it was only dark in the sense that there are cannibals, Nazis, kidnapping savages, etc. The book was very oddly supernatural in places (although it's not clear if it was actually supernatural or not), and I don't think it fit with the rest of the book. 
 As some other reviews mentioned there are a lot of deus ex machina type situations, but they didn't bother me, and the author/main character makes reference to them several times. The way the author had his main character examining his own story was great, because they were the things I was already thinking. Those parts reminded me of Stephen King's Dark Tower series. 
 The ending was very enjoyable, and I almost gave another star for that except it was pretty sudden with not really much buildup to it.