Not bad
Kept me playing for about half an hour, which isn't common with games on NG.
Improvement issues: Consider using a spell-checker.
Also, the "repair" function just wouldn't seem to work for me. No idea why.
Third, the controls were just a little sketchy, the upgrade window thingy should be a little easier to get rid of or work around. Perhaps a stationary window with all of the tools to upgrade that just modify the highlighted block rather than the window appearing over where you click.
Fourth, The sound was a little dry-- but that pales in comparison to the lack of music. Needs to be more lively and urgency inspiring if possible.
Fifth, The art was a little drab, but clearly that wasn't your focus, so that's okay. Maybe you could find someone to give you a little help with the art issue, I'd help ya but I have final coming up, let me know when you're going to make a 3rd game and I might be able to do some drawings up for you (I'll check and make sure the contact info in my profile is current)
Sixth, (and finally) the prices on the guns at the bottom didn't seem to be formatted correctly, and some of the upgrades didn't have a label on the amount of upgrade you actually got out of it.
DESPITE all of my bitching and complaining, I loved it. And I'm only trying to help you out, don't take any of the preceeding the wrong way. Very nice work.