GoodReads Summary: The Earth's leaders have drawn a line in the interstellar sand—despite the fact that the fierce alien enemy that they would oppose is inscrutable, unconquerable, and very far away. A reluctant conscript drafted into an elite Military unit, Private William Mandella has been propelled through space and time to fight in the distant thousand-year conflict; to perform his duties without rancor and even rise up through military ranks. Pvt. Mandella is willing to do whatever it takes to survive the ordeal and return home. But "home" may be even more terrifying than battle, because, thanks to the time dilation caused by space travel, Mandella is aging months while the Earth he left behind is aging centuries.
After I finished this book I had to ask myself why I never read anything else by Haldeman.
In a way, this book seems to be the counterpart of Heinlen's "Starship Troopers": While Heinlein shows how smart the army can be, Haldeman seems to show how the army can be pretty stupid sometimes.
It follows the story of William Mandella, who gets in the very first war against an alien race that suddenly destroyed a colonizing ship. Due the way humanity uses to travel the unverse, what happens in just a few days/weeks to soldiers in-route, the everyone on Earth it takes years if not decades. So, in the end, although Mandella gets into only 3 battles, his time on the battlefield (well, on the way to the battlefield and back) goes around 900 years.
Also, there are some very clever things Haldeman did. At the very start, I thought the story was a bit sexist. It turns out it was a very well thought point Haldeman did to make a very long arc -- more like a criticism of the sexism in the 70s than some hidden agenda towards sexism.
If I didn't had just read yet another book about wars, I'd probably keep going through the series. But I guess I deserve a break after going through two different wars.