Hey Vincent,
I just checked your smashwords preview of the book in question. I see the simplistic writing style that your reviewers are talking about, however given the narrative I think you should leave it as is.
Since it's told from a first person perspective I can get the point of your narrator actually, literally NARRATING the tale. The simple prose and almost Joe Friday like style works for me in the context of what I'm assuming is a kind of military science fantasy.
If you're determined to break the style and expand, then edit your next writing how you see fit. But, this stuff seems to work in context.
In the interest of full disclosure, I only looked over maybe the first six or seven pages. And I could see some things that you might want to improve in subsequent volumes
