This game is just about perfect!
I can't say anything truely bad about this game.
The gameplay is fun, the level design is great, the story is amusing in the way that it's almost mocking it's own existence in a simple shoot-em-up, there's plenty to buy, the gun upgrades aren't all linear (it all depends on your playstyle) and each of the weapons plays kinda different.
It does lag a bit when there's rebounding bullets at high speed everywhere with multiple monsters around, but it might just be my computer not being able to handel it. I noticed the game only starts me at Medium Quality, but even at Medium Quality the game looks great. I can only imagine how great it looks on high quality.
Even with the upgrades, though, I never felt like they made the game too easy.
There was a good balance between the weaponry you could hold and the difficulty of the enemies. Right when monsters seemed a bit too easy due to your new weapons, they got harder.
The only other "complaint" I can add is that you max out your Level early on and that there's no real point to collecting XP after that. However, even then, the bonus moves you earn really help to have on those levels, so it balances out again. Another good point, not a single learned skill went to waste, I made use of all of them. Sometimes in games, you gains skills and they are rare to use or plain out useless. Mostly for show and you don't need them. I deifnatly made good use out of every skill learned.
Frankly, I couldn't stop playing this game, I had to beat it the first time through. I got to the last level, but had to quit eventually when I couldn't beat it... and I had just been looking at the agme too long. :D
All the same, it was addictive.
Very fun, very fast.
It was such a nice, well made, well polished game that it could have been a console game.
Good work and this deserves the best score I can give it.