The tight ammo situation in the first part is likely the result of three items falling out of the level.
Pretty basic but okay overall, good for a first release and a promising start. Could have used a little more activity in the final part, when returning to the previously visited area.
I didn't find the unmarked secrets. They appear fairly random and without clues. Too much armor, indeed. I agree with otp's and Shambler's points.
in case the author ever stumbles upon this thread.