I got to level 6 and decided to stop playing, sorry. ;p
I was pretty irritated at the fact that you said "large levels" and when I was playing it seemed like really small levels.
It wouldn't really be hard to be the ACE of killers in my opinion. Something that could easily change that is by having actual ammunition instead of infinite. Also, actually upgrade your enemies. Make them do more damage or something.
It seemed each level blended together, a lot. Try to make a couple new original maps and at least 3 more new enemies that are original.
You could also spruce up the storyline a little bit, but that's just me (I'm a nut for story ;D).
The armory definitely needed more than 2 guns and one of them is already unlocked for you.
I did however like the trophy idea and you should be proud of that. ;]
The loading screen really through me off...
newgrounds.com — Your #1 online entertainment & artist community! All your base are belong to us.