It's often cited as a science fiction classic, and I can see why. It's a book about war, but that neither glorifies it nor rants about its awfulness. In fact, very little of the narrative space is spent on the battlefield -- the stance it takes is instead the terrible waste of lives and potential, shown sometimes in the deaths of characters significant to the protagonist but just as often in a quiet sad awareness of the things his fellow-soldiers would be achieving if they weren't being trained and sent out to battle.

There's also some pretty hokey future-culture extrapolation going on, making use of the relativity effects of waging an interstellar war to highlight the alienation of a soldier returning after a tour of duty.

I must admit, it seems pretty dated to me. But maybe a simplistic "war is difficult and painful not just when you're fighting" message is a good antidote for the more strident "war is hell" and "war is necessary" voices we tend to be more familiar with.

Recommended, but partly historically, because it's an acknowledged classic.