I picked up The Forever War last spring based on the recommendation of John Scalzi. Specifically, it was required reading for the characters in Scalzi's book The Ghost Brigades. I am very glad I did. This may be one of the most cosmologically accurate sci-fi space battle novels ever written. Cosmology as in the study of vast tracks of the cosmos. It certainly is the most accurate I have read. The way in which Haldeman treats the interstellar distances and the time-distortion are central to the main plot and he handles them very well.
The Forever War is the story of one soldier thrust in the middle of an interstellar conflict that from his perspective doesn't last very long at all. But in the time stream of Earth, the war lasts more than a millenium. Because of the enormous distances that the military must travel, near light speed velocities cause great time dilation to the crews. Each mission lasts hundreds of years, but is only weeks in their perception. The plot is centered on the war, but the real story is the feelings of loss and displacement that the soldier experience when everything they know is centuries gone every time they return.
I suspect this is another antiwar novel. However, it is subtle enough to not be a problem. I enjoyed the story and have also read its not-really-a-sequel Forever Peace. Joe Haldeman's style is different than most sci-fi writers in my opinion. He seems much more formal and precise, more "educated" even, but not to the point of distraction. His work is actually pleasurable just to read. For reference: I stopped reading Steven King many years ago because his style degraded to the point I couldn't force my way through the words to get to the plot anymore.