This film was made within a year or so after the real event with many "actors" being the actual survivors. It shows a very narrow slice of Operation Market Garden, but, think of it in the context of one of the participants - they had a very limited view of the big picture - they were just trying to survive and achieve objectives. Yes, a few errors, but what film doesn't?
Some reviewers say the acting in stilted, but it was not acting, they look like real men doing real feats of staying alive and bravery, not some polished actor-twit. One of the most important reasons for keeping this film preserved as well as any supplemental film cuts, both real combat archival and re-enactments, is that the uniforms, personal gear, weapons are period correct. Nothing worse than seeing a 1950's rifle in a WWII film. The dialog is period correct, again, not some script writer's idea of what was said. Breathtaking film of close packed airborne formations, how tight they really were. The use of real film to show the parachutist sticks in close form, not the staged and safety mandated situations. It allows those of us who are history buffs or perhaps collectors of memorabilia a source where we can stop the film and closely inspect items of interest. And the re-enactments using real men versus stunt-men, were eerily dangerous and realistic, something that could not be pulled off in today's regulated world. The accuracy of the radio procedure, including the radio telegraph key proper usage and background code being actual message segments, is heartily appreciated.
Some may say it is stilted, dry and not a real action "shoot-em up" but that is precisely this film's value. The big screen "A Bridge Too Far", with all of its faults, gives a better story line of the extent of the operation and lets viewers understand why the poor blokes in "Theirs Is the Glory" were seemingly left to be hung out and dry (die). I personally think for a modern student of military film, "A Bridge Too Far" should be viewed first, followed by "Theirs Is the Glory" and a few other earlier films to get the real nitty gritty close in action. The use of the field reporters and skewed information represent at-the-moment situations. No one has a hidden foregone conclusion. It just happens. Kudos to the Dutch civilians who were able to participate so soon after the horror, it brings a real sense of understanding to the trauma of their private war-hell. Love the classic and understated British "stiff upper lip" tenacity. The lines that may have seemed cheesy and poorly delivered - well, they are closer to reality than what most Hollywood directors would ever allow. (Incidentally, I am a Yank, not British - so I can slam Hollywood quackery all I want without a perceived national bias)
After all, these were the men, the real men - "those filthy, grimy, wonderful gentlemen who dropped from the clouds to fight where they stand... ... ... Just ordinary men."