I was somewhat taken aback by the style of this novel at first. After reading a few dozen pages, however, I could clearly see why this book is considered classic military science fiction. This is a fascinating contrast to Starship Troopers.
Haldeman's style is terse and effective, seasoned with a sly sense of humor throughout. The protagonist, William Mandella, is a likeable military everyman with whom a reader readily identifies. The battle scenes are particularly well done, allowing a reader to easily follow the action without the confusion that would plague a less skillful account.
The Forever War is notable for its exploration of the temporal effects of faster than light travel, i.e., Mandella's tours of duty last hundreds of years on earth, while for him, only a few years pass. Mandella goes forth to battle, having no idea what type of home will await him in the unlikely event that he survives. Eventually, Mandella is rendered a human anachronism, a veteran in command of troops he can barely understand.
The parallels with Vietnam were mostly lost on me, as I'm too young to relate, but the theme of coming home to a world one no longer recognizes is more than ably developed. Another theme that gets a lot of play is that of the unintended consequences of social engineering as Earth's society "evolves." Some of the changes to Earth that Mandella witnesses are disturbing, many are humorous, and the final chapter is extremely unusual and thought-provoking.
More than just a cold military fantasy, The Forever War has a surprising emotional impact as well. Best of all, Haldeman makes his points with subtlety and humor, not by nailing them into your skull. A terrific read that I would recommend to anyone without hesitation.