Haldeman's "Forever War" is often compared with Heinlein's "Starship Troopers" but I think the similarity is superficial and both stand in their own right.

In "Forever War" the characters have a very jaded and weary look on life, military service and the war they are involved in, something probably influenced by Haldeman's own experiences in Vietnam.

I find Haldeman a little hit-and-miss sometimes, but overall "Forever War" is one of his best. Good characterization, good central theme and uses the consequences of time-dilation to great effect.