Haldeman's The Forever War has garnered a lot of praise and awards over the years, and is particularly lauded for it's anti-war themes.

The parrallels with the Vietnam War situation are obvious and there are quite a few points made about the stupidity of war, 'military intelligence', the dehumanising effects of battle, the dislocation felt by returning soldiers (made even more so by time dilation), and the difficulties of fitting back into a society that doesn't understand where you've been and what you've seen.

But for all that the tone of the novel is eminenetly readable, told from the laconic first person viewpoint of William Mandella, never preachy, and despite the fact it appears to come from a diametrically opposed political base, it reads like a modernised Golden Age Heinlein military SF romp.