The Forever War is one of the classics of Science Fiction - a book known to almost everyone who reads SF. I read it many years ago, and have recently been working my way through many of the better SF books of the past 50 years.

Our protagonist is William Mandella, a conscripted soldier in an already outdated future (it was written in 1974: some of his ideas of the future are already clearly and blatantly wrong). After mankind has expanded to the stars, they've encountered the Taurans - and a war immediately ensues. Haldeman postulates faster-than-light travel - but it still requires 90% light-speed pre- and post-FTL jump. Which means you lose years of time. So the war stretches across centuries, and soldiers often return decades or even a hundred years after they left, so they don't understand the culture of the world that's still sending new draftees ...

Haldeman's views on homosexuality were probably quite enlightened for the 1970s, but come across as a bit dated and unpleasant in 2018. The technology around computers is of course somewhat dubious. But overall, the book still ranks among the best of military SF novels, a dark tale of history completely bypassing soldiers, abandoning them to brutal culture shock when they return to a home planet they don't recognize generations later. The ending is surprisingly abrupt and upbeat, and yet oddly appropriate to the book. This deserves its place among the best SF novels.