This work reminds me of Battle Royale, which is great because I loved it and have always wanted to read something like that again. Apart from the play or die situation with kids, there's not much similarity in plot or even atmosphere, but I love that both works focus on each character and we get to know each character intimately. That's what makes survival or apocalypse works awesome for me: the relationships between characters, how they interact with each other, how they think, and how they make the decisions they did.
While Battle Royale explores morality, the decision of whether to play the game or not, friends banding together or turning on another, Bokurano is a quieter work and explores existential questions. The battles in Bokurano are mere plot devices for the characters to explore the meaning of life and other philosophical questions. After reading it, I just felt empty and hollow, which is in line with its existential themes. I don't think Bokurano will make most readers love it, I certainly can't say I did, because you're not supposed to find it "entertaining" or "exciting". It's a journey for both the characters inside the manga and the readers. You will certainly think and reflect on life as you read Bokurano.
Most survival mangas build up momentum toward the climax and the end but like I said, Bokurano is a quiet work. In other survival mangas, you don't know who's gonna die next and that's where the excitement and the momentum come from. However, in Bokurano you know who's going next and all characters have certain death on neck. No matter how much you're rooting for them, they're going to die. Thus, the tone of the manga can be very depressing for some, but Bokurano doesn't glorify the depressing atmosphere; rather it's about finding hope and meaning in face of the finality of death and the futility of life.
I would recommend not to marathon it because like another reviewer said, it could make you numb to the characters' plights. Once you don't sympathize with them and their impending deaths anymore, it will sap the meaning away from the manga's message and the discussion on life and death. Instead, experience it little by little as you also reflect and find your own answers to the questions the manga posed.