As an Exit game it's fine and fairly typical of Exit which I liked. As a book/novel... not good.
Lets talk about Exit as a book. I've played many (almost all) the Exit games with my family so I'm familiar with how they work. That being said, the instructions and layout of this was iffy. Unlike the games, there are no clear stop signs telling you not to turn the page until you solve the puzzle. Somewhat confusing, but I guess there's common sense to help us assume that the big bold font means to stop. The beginning also did not state that I was allowed to and supposed to look at the codex in the back to use for solving the puzzles. So I feel like these things could've been related more clearly to the reader.
The puzzles themselves were much like every Exit game... some good and fun with the right amount of difficulty. Others that just had stupid concepts and pissed me off. Which is subjective I suppose, but it is what it is. Also I do wish there was less cutting. I'm fine with it I the games but in a book it was just a pain. It's not even about reread ability, it was just simply difficult and annoying.
Ok now about the plot and characters. This was so not even lukewarm. Which is fine I guess because its primary function is to be Exit but... to put this into a novel format is to set my expectations high. I wanted to read an immersive novel where I also had to solve puzzles myself once in a while. Unfortunately this was just your average Exit flavor text switched from 2nd person POV to 1st Person with some beefed up dialogue and descriptions. The ending and climax is massively underwhelming, there are no explanations for anything really, nothing is satisfying. Characters have 0 depth or arcs or even distinguishable traits. Theres nothing particularly grabbing about the writing style: it's not scary or atmospheric or funny. It just is. Like I said, you read this for the puzzles and that's perfectly fine, but this could've been so much better.
All that said... I'd still eagerly read another one. I do love the Exit franchise.
I liked the puzzle parts, but I felt like the plot between the puzzle parts wasn't very compelling and there were too many interchangeable named teens to keep track of for me. But I still enjoyed reading it.