I think you need to convey more of what the characters are thinking. You should probably sacrifice some of those lines of dialogue you find extraneous. Take the points in the story you think there is too much dialogue and write it differently so it isn't extraneous talking. You've got a story in your head, true, and it's developed nicely there, but you have to find a point in which to develop the characters, and develop the build-up of the plot.
All in all, I like where you're going in terms of story, but it seems the story itself (and characters) could use some development, if at all, some.
"The Private turned the corner hesitantly, only to find himself face-to-face with a Klorbinean. It was dead and hanging by its torso from the ceiling by some sort of ooze, but the Private didn’t register this at first. He stumbled backwards and fell flat on his back." This was the height of the story, add more stuff in that explains and less stuff in that talks. This is a good piece of writing.