(I'm coming back to review the first volume after completing the whole series, in order to give people a better idea of what to expect, without spoilers.) If it's not already clear to you, this is an escapist, wish-fufillment, self-insert fantasy for freedom-loving gun-enthusiats (to use the least pejorative phrasing I can come up with). You will only appreciate this manga if you can get invested in the technical details of the weapons used and the tactics employed. I certainly did. For example, the author goes to great lengths to explain why at no time can anyone in this war use lasers. Everyone must always use bullets. It's badass.
While the plot may seem like it's moving in a direction that it might critique itself and the tropes and themes it uses, do not hold out hope for this. The story makes it's moral claims early on. Gundam gundam gundam, with great power, war is hell. From then onward, it's full steam ahead, full genre, no self-awareness.
Some trigger warnings:
This story includes some disturbing sexual content. While anime and manga fans may be expected to be generally desensitized to seeing some mild female nudity (which this story is by no means short of), Exaxxion really pushes past what I was comfortable with by including a highly graphic depiction of sex between a prepubescent girl and a teenage boy, and also the rape of an adult woman.