Graphic : nothing new. I like the desing but it lacks originality. Store Clerk is kewl though!
Music : Not bad. Catchy song for the level and heavy for the sub bosses.
Gamplay : Not the best i've seen. I think you should work on the UI and the mouvements a bit more. Overall it's "ok".
Is this really your first flash game? Because it's pretty well done. If the other maker of this game have more knowledge sure, but it's uncommon to see such detailed perfomance on the first try.
I like your game. Work on it a little more and add some effect. Maybe a quality setting? Voices could be a funny add on with the bosses. Make the girl's chest "bouncy" ? That's my own perverted suggestion, don't mind me =P
Store Clerk could be an interactive character. i mean what if clicking on her produced some side-effect in the game? (Faster mouvement speed, better jumps. etc) with a % of chance happening.
I found some glitches and bugs here and there. Here's a few of them.
When you jump, you can shoot below the ground level.
You can double and triple jump using the rocket launcher and a breakable object.
When you switch weapon very fast and don't release spacebar, you get the infinite rocket with machine gun speed while carrying the gun sprite. Was kewl on the last boss.
The gun glitch can also make the game crash or freeze.
Replaying a level with a bosse will make that boss reappear.
One of the level (not the end level) doesn't have the white mask. Sorry i dont remember which, the game is currently frozen for me atm (too much gun glitche)
I think that's about it. Work on it a little more pal! i'm sure you can get a helluva good game with that!