Perhaps it helps to remember...

Rating: 2/10 (4 November 2009)

that "Jarhead" is based on a book written from one man's point of view after serving as a Marine. I suspect that the movie (and book) say more about Swofford's personality and what was meaningful to him during his service than what the Marines are actually about. I have not served in the military myself, though many friends and acquaintances have. They confirm many of the factual aspects of the film, but demonstrate a completely different understanding and perspective of the experience.
Does military service include long periods of boredom? Sure. But just think, for example, of the number of troops in WWII who spent literally years away from home, with only written correspondence to connect them to friends and loved ones. Many of those NEVER saw combat and (quite frankly) may have had little or no effect on the outcome of the conflict. Not all Marines (perhaps not even a large portion) ever fire their weapons in anger at an enemy.
Ultimately, my impression is that Swofford has the type of selective memory common to many college students, who seem to remember the drunken parties, the sex, and the fraternity hazings best. Other students remember the more valuable aspects of the college experience, especially when they appreciated the opportunities at the time they attended college. I suspect that Swofford is accurate and factual in most of what he describes, but it does not paint a complete picture of the Marine experience anymore than a John Wayne film does.
OK, back to the film. It's also boring as hell and should never have been made by Mendes. There is no need to watch it.