Halo: Ghosts Of Onyx by Eric Nylund
This book is part of a "Halo" series of books, but it can be read as a stand-alone novel. The book series is associated with computer games. I am totally unfamiliar with the games and, as best as I can tell, it has not affected my reading of the book.
The major premises of this story are:
1) There is an interstellar war with aliens ("Covenant") who are believed to want to wipe out humanity,
2) There is an elite branch of Earth's military ("Spartans") who are trained as children and then medically augmented to be super soldiers,
3) The Spartans are training on an obscure planet ("Onyx") on which is burying an ancient, powerful alien technology,
4) On some planets remains of technology from some disappeared civilization ("Forerunners") has been discovered. They appear to have developed systems with the purpose of eliminating all life in the galaxy. These artifacts play a role in the religion of The Covenant.
I can't imagine how this would not be "military SF", however it doesn't feel exactly like military SF. To use an imperfect analogy, Ender's Game is all about military training and conflict, but it's not typical military SF.
Military SF is not one of my reading priorities; however I do end up reading some of it. Partly, there's just so much more-or-less military SF out there. I had heard positive comments about this book and I was curious to read a book by Nylund. So I gave it a try.
We see some Special Forces-type battles by Spartans, training of Spartans, guerilla warfare by Spartans, planning by military leaders to develop Spartans.
We do eventually get a look inside the Covenant. It's certainly not as in depth as our familiarity with the human forces. The Covenant includes several alien species. We see some about their physiology and their occupation niches in the Covenant forces. We learn some about the Covenant's technology and religion.
Reading the book gives a sense of being immersed in another universe. Nevertheless, I wasn't left with that much that lasts with me.