The prose, I would describe as Beckettian - not in the sense one usually hears it (which generally seems to mean anything "weird"), but in the sense of that peculiar detached voice that is simultaneously incredibly poignant and strangely elegant while being immersed in the shit of life. There's a kind of hushed reverence alongside an awareness of horror, I don't even know how to explain it. It's also, of course, darkly humorous while being frequently tragic. This is the kind of sentimentality I can really appreciate - not cheap and treacly, but rather more hard-won and bittersweet.
The plot is also quite fascinating. It's actually kind of a modern take on Of Mice and Men, but with Irish soldiers fighting in World War 1. So one thing that's interesting about the book is that it depicts the experience of Irish soldiers fighting on the British side - something you've probably not spent much time thinking about (I sure as hell haven't), but it's a knotty issue, fighting alongside your oppressors. It's also, more generally, the story of two boyhood friends, and even more so, a kind of coming of age story of a really compelling narrator.
Really, a riveting book. Highly recommended.