This is the only science fiction novel I've ever read that deals with how relativity would affect faster than light travel, and it does so in a way that felt very realistic. While our narrator, William Mandella, is deployed on missions that take him a few months or a few years, hundreds of years may be passing on Earth. Huge societal shifts have happened every time he returns, and he very quickly leaves behind everyone and everything he's ever known.
Mandella himself is a great character, and his narration is fantastic. I appreciated his occassional bursts of dry wit to lighten up a heavy war narrative. I also appreciate that he doesn't dwell on the sometimes gory aspects of a military campaign. I can imagine them for myself, and I don't need every last detail. The science fiction elements are well thought out, and thoroughly explained without getting too bogged down in physics that I'm not capable of following.
There's good news and bad news about how Haldeman treats gender and sexuality in his future army. The good news: women are for the most part treated as capable and professional soldiers, with no apparent difference made in combat expertise or rank. Awesome. Also good: in his future Earth, where homosexuality is encouraged, he has lesbian and gay soldiers serving equally and without fuss next to heterosexual soldiers. Still awesome. The bad news: outside of battle, the women are expected, by regulation, to be sexually available for the male soldiers. Sexuality is officially changeable, and the happy ending involves two of the main gay characters being changed to heterosexual. All of that really bugged me, for reasons that should be obvious.
I can cut the book some slack for being 40 years old. This is why it's on my "product of its time" shelf. I feel like Haldeman was trying to do justice to the gender and sexuality politics he plays with. In the end, that's why I'm able to give the book four stars. It's an excellent book, with a few scenes that are irritating to me but which were probably fair for its day. And who knows, maybe if the narrator of my audiobook hadn't decided to go with a stereotypical voice for the gay characters, it might have helped.