: It follows William Mandella, a soldier fighting an interstellar war against an alien race called Taurans. Due to time dilation from near-light-speed travel, Mandella ages only a few years while centuries pass on Earth.
: Follows elite Space Marines in a "Universe 13" that is falling apart. It mixes humor, RPG progression mechanics, and battles against green alien threats ("Ksenos").
This is a seminal 1974 novel inspired by the author's combat experience in the Vietnam War.
:If you want a deep, thought-provoking story about the human cost of conflict, go with Joe Haldeman . If you prefer a "useful" exploration of leadership and historical "what-ifs," Sergey Karelin's series is the better fit.