Hardfought, by Greg Bear. Sci-fi set in the far future, spoken with a military patois that is difficult to understand but is meant to highlight the alienness of the forever war that the story takes place in. Themes upon themes fifteen-plus layers deep, even though this is only a novella.
I have something north of 3,000 volumes in my library, and if I was to pick the most influential fiction story of my life, this would be it. I had difficulty reading it as a teenager who was typically reading at a university level while in high school, so it’s going to take serious effort by most to truly benefit from it. But when you finally understand those themes… holy shit.