I'd probably raise that on Gibson. It's one of the best books, period.
"The protagonist, an almost-anagrammed stand-in for Haldeman named Mandella, is hurled across far reaches of the galaxy to fight a poorly understood, apparently undefeatable foe."
In that regard, it's as much a commentary about war today as it is the future.
I found it a bit 'thin'. Perhaps that was intentional as a corollary to the breakneck pace of time-dilation Mandella faced and the societal change he faced. I always felt out of place and behind as a reader, never really finding myself fully immersed in the story Haldeman was telling, always wanting to stop and see more about how things had changed. I guess the 'world building' wasn't as good as I hoped for.
The Forever Peace on the other hand seemed to painstakingly explore the build up to societal change, then ended as it was about to happen.
Either way, both frustrating books.
Likewise. Which is not to say I thought it was bad. I think perhaps it was a product of its time? I could imagine it felt a lot more urgent and prescient when it was released than it does today (I read it for the first time earlier this year).
Personally, I found Use of Weapons by Iain M. Banks to be much more compelling when it comes to a sci-fi study on the nature of war. Each to their own, of course.
I think the rationale is really that Haldeman was really commenting on the pace of social change, especially for service personnel, particularly those who served multiple tours. The protagonist hates the horror of war as much as the alienation from the society he is allegedly being forced to defend.
Though I can see why that puts some people off :)
I think that this was a conscious choice by Haldeman - he wanted you to feel as lost as Mandella, who got a brief glimpse of a culture before being plunged yet again into another relativistic journey into the future. The only constant in his life was the Army, as inhuman and brutal as it was. I thought it was a good choice, but I can definitely see why you'd be frustrated with it.
I enjoyed reading it, but didn't think it was particularly great (same with Forever Peace, though that book had somewhat different issues).
It's worth mentioning that Haldeman wrote it in part as an allegory to Vietnam. It's often called a counterpart or "rebuttal" to Heinlein's "Starship Troopers", though you'll read that both authors had immense respect for each others' books.
In any case, I agree, "The Forever War" is up at the pinnacle of the art of Science Fiction and a near-perfect example of the message it can deliver.