@Vertigon: Well... Bad news, or very bad news, soldier?... WRONG ANSWER!... I can't hear ya!... That's right, here's your very bad news for your hardcore marine ass, because the Empire doesn't need any other kind of ass!... WHAT ARE YOU LOOKING AT? GET GOING!
Nice development of the story, and nice twist in the end. This goes a long way to keep readers interested, making them think and wonder.
Your biggest fault, as I see it, is genre confusion. You've got a verbal conversation in mind, but, possibly, literary clichés make you try to write a regular action piece. Verbal conversation requires believable language, and not only in dialogue, but throughout the story. And, well, I'm having a hard time imagining an ex-con soldier start his story with "In the dim glow of dawn..." In a first-person piece, in general, language is very important. If you do it wrong, the reader's reaction may range from "Is he joking?" to "Hm... Experimental pieces aren't really my thing." As a fiction writer, you have to be an actor inside, so my advice if you're going to work on this piece further, would be to try to get into the shoes of the protagonist, put on a funny accent, and tell this same story, addressing an appropriate audience. Maybe some jargon to taste would be a good thing.
And while you do that, pay attention to dialogue-tags. It goes without saying that no one speaks like that in real life. More importantly, no one writes like that. Your dialogue-tags attract a lot of attention. I at first, after getting to "I exclaim", read only the dialogue tags. It may be because in your dialogue they're so redundant that they are a part on their own, so if you omitted the dialogue leaving only the dialogue-tags, you wouldn't miss anything. Keeping both parts is probably a bad idea, and I'll leave it up to you to decide which one you like most. However, if you decide on characters' words, a way to reduce the prominence of dialogue-tags lies in simplifying them. "Exclaim", "snarl", and "concede" are pretty fancy. Simpler substitutes are "say", "ask", "reply", and that's pretty much it. Well, "shout" for very tense situations... Hm, I lied. Technically, you can keep both parts, but you have to turn the dialogue-tags into separate action lines. That is, instead "snarling", Jun would glare at the protagonist, lowering his gun with a hidden threat, probably.
My biggest gripe, however, is that the story is in the same old space war, planet under orbital bombardment setting. Although, I suspect that it's related to some video game which I haven't played.