It is not often that I struggle to find something to say about a book. If it's great, I can give a list of reasons why. If it's terrible, I can say why. Even if a book is mediocre, I can share why I think that is the case. The Forever War by Joe Haldeman, however, is so unmemorable and placid I'm really struggling to say much about it at all.
The one element of the book I do want to make mention of is that the book's use of time and space travel was a unique way to emphasize the idea of a forever war. As soldiers rocket across the universe they age more slowly than those on Earth; this leads to some interesting dynamics as soldiers try to re-acclimate to Earth-life, which is especially difficult because it might be 50-100 years after their initial departure instead of only a few years. As a commentary on the Vietnam War, the book works fine. Although, I would much sooner recommend The Things They Carried by Tim O'Brien than I would The Forever War. In addition to being a commentary on the Vietnam War, it also is a commentary on the army and military life. But yet again, I would point to the ultimate commentary on the military, Catch-22, instead of The Forever War as the book which really has something to contribute.
As a work of science fiction, the book is fairly unremarkable in my opinion. The writing, the world-building, it's all so consistently sterile and flat nothing left a lasting impression. I don't dispute the creativity of the book or the considerable thought that must have gone into it; I just didn't find it interesting or meaningful enough to make a difference to the overall story-arc. In a way the book is its own activity of attrition as you push yourself to finish the book while losing motivation after each page.
I didn't care for The Forever War, obviously. It wasn't necessarily a bad book; it simply made no impression. When reading books and experiencing stories, there is not much else I could say as a harsher criticism. I didn't care; therefore, I won't remember.
Other Topics of Interest:
Reflections: The Things They Carried
Reflections: The Moon is a Harsh Mistress
Page-Turners: Black Hawk Down