Okay, for a book this size, it took me longer than usual to finish it, and the reasons behind that (aside from real life obligations) I have taken the care and time to explain below. However, before I get started on it, please know that not everything I have to say about this novel is negative; it has its positive aspects too, which I'll touch on after the fact.
So, let's begin in list format:
-Repetition.
-Superfluous exposition.
-Info-dumping at points.
-Telling instead of showing.
The four aspects listed above didn't occur once or twice, but repeatedly throughout the novel, from beginning to end. There were times when a character would think, say, and then another character would reiterate the same piece of information--all on the same page. Sometimes even within the same paragraph. Not only did much of this contribute to the book's size, it became incredibly irritating, considering even if a reader didn't catch on to subtle hints, the information was given bluntly anywhere from 3-5 times in very short order. With regards to superfluous exposition, there were times when it went into great detail about characters' backgrounds, thoughts, etc. when it otherwise was unnecessary. This also more or less covers info-dumping; several times, info was given that had little impact on the characters' actions or motivations, but that isn't to say every instance of info being given was for naught--just that it occurred more than what was necessary. Telling instead of showing is pretty self explanatory: at times, we are told (sometimes by the characters) things we otherwise could have learned from their actions, tone of voice, etc.
Other aspects that came off jarring: awkward dialogue/inner monologue at points, some of which felt incredibly forced and unrealistic. I get that people sometimes think about the most inane things while in the middle of serious situations, but I felt these aspects either could have been 1) toned down, or 2) worded differently so that they didn't come off as awkwardly.
I also found the over-usage of "crushes" being mentioned a bit tedious. If it had only been a few characters (or couples), I could have dealt with it. But it seemed every time I turned around, crushes were being used as the motivation behind the majority of characters' actions; motivations for what they were doing in the "game", and motivation for their dialogue. Overall, it got to be a bit much after a while.
The frequency of the student numbers and gender being displayed in brackets became a turn-off very quickly. While I understand certain occasions did call for the reader to know a specific character's designated number, it really didn't need to be displayed as often as it was throughout the novel.
Characterization: This was a bit hit and miss for me. While some characters were well developed and grew with the plot, others felt like cliché archetypes in anime. Considering this novel is written by an actual Japanese person, this was even more disappointing, since this kind of thing is what one would expect from a hard-core weeaboo, not someone actually born of the culture. Following on the tails of characterization, it also became redundant when so many male characters kept underestimating their female counterparts; whether because they, in their naivete, believed the best of them, or because they assumed girls couldn't be as violent as boys (no matter how hard-boiled the reputations of some) it turned me off a bit more. When it was Shuya, I accepted it as being part of his character. But when others echoed his inner monologue? Suffice it to say, I found it a bit unimaginative, having so many characters thinking along the same lines.
Now, complaints aside, I felt the overall plot was well-handled. Environmental details (while overwhelming at times in their clinical explanations) were otherwise well done. Details about the Program (in which the students find themselves thrust into this sick and twisted game) was likewise well laid-out. As the story progressed, I found it easier to relate and sympathize with some characters, and the suspense during intense gunfights--especially featuring characters I had built up something of a liking for--had me holding my breath at times. The syntax was hit and miss, but when it was hit, the storyline flowed really well, and at those times, it was easy not only to imagine the characters' surroundings and situations, but to immerse myself in it. In other words, I became emotionally-invested...but only *when* the writing was spot-on.
All in all, while not the best read, it was far from being the worst. If I could give a split rating, I would give it a 2.5, but 3 likewise seems fair.
Would I recommend this book? Sure. But I'd also caution the reader to temper their expectations.