I agree with the reservations that earlier posters have raised about military SF, and why I've never really got into it. To begin with, I get the feeling that a fair proportion of it is simply “X Soldiers In Space”: usually the US marines, but sometimes one of the armies that pop culture inaccurately depicts as superhuman: Vikings or SS or Spartans or the like. I’m not sure that this makes for good SF where the setting is skewed to give the super soldiers the chance to be awesome. Only an idiot would fight a giant robot space-knight face on; he’d blow up the stores where the space knight kept the spare batteries for his Suit of Uber-Mecha-Awesomeness, sneak off and wait for him to run dry. And then push him over. Also, even leaving its politics out, I think Starship Troopers is a boring book, and I’m wary of a genre that sees it as one of the sacred texts.
In fact, one of the most convincing SF books I’ve read to deal with the military isn’t a story in the usual sense: Lee Brimmicombe-Wood’s Colonial Marines Technical Manual, which is an attempt to give back-story to the setting of Aliens. It actually covers problems of supply across space, logistics, budget and so on as well as just how great the soldiers are.
Of course, I don’t want to suggest that all military SF is as I’ve described and I don’t want to rubbish it as a genre, just that I’m wary of wading in because a lot of it probably isn’t to my tastes. I may well be unfairly tarring it with the same brush. Also, I probably have no right to say this. I’ve written for Games Workshop and the working title of Space Captain Smith was “Space Biggles”, but there’s a level of tongue-in-cheekness there which hopefully helps.