Private William Mandella finds himself fighting to defend an earth which has become more alien than the extra-terrestrial foe he fights.
Deep space flight, wormholes and relativity, mean that for every tour of duty he survives, although only months long to him, centuries pass on earth. Forced by circumstances to continue fighting, Mandella becomes detached from humanity in every way; emotionally, culturally and even sexually, until, the oldest man alive, he is transformed into a figure of ridicule and discust by the new generation of soldiers joining the conflict - soldiers which he now must lead!
Joe Haldeman has taken his own experiences of combat and the aftermath of the Vietnam War and turned them on their head. While the veterans of that conflict returned; profoundly changed, to a homelife that had barely moved on, the combatants of the Forever War come back to an earth which has altered in every way, while they have stood still.
Nicely paced and defly executed, Haldeman's unfussy prose leads the reader effortlessly through the story to a most satisfying conclusion.
Millennium's SF Masterworks series is a fantastic collection of books, and the Forever War is paramount among them.