Not bad for a first game.
Graphics: Ripped Doom sprites on simple vector backgrounds. Moving gun and crosshairs like that ad banner at the top of this page. Would be better with original graphics or some juicy smoke, sparks, and debris where the user clicks, and blood if they sucessfully click an enemy. This would involve some pretty advanced AS, though. Spawning multiple objects isn't very intuitive in Flash.
Style: Not bad. Considering that this is all done with buttons and some VERY simple life meter AS, it comes surprisngly close to capturing the feel of an old FPS. Some low-key music would have been nice, as well as moving enemies, projectiles, or pretty much anything else you don't know how to do yet.
Sound: BOOM! *ka-chick* BOOM! *ca-chick* Sounds from doom are used to good effect. The shotgun reload sound actually is a good indicator of when you can fire next.
Violence: Fleshy beings explode into piles of gore when shot. It doesn't get much more violent than that... oh, waith, this isn't 1991. This is Newgrounds, Circa 2005. OF COURSE it could be more violent.
Interactivity: Not bad, for a button game. Pretty darn decent. This kid known how to imply gameplay where you would think there is none. Here's hoping he works hard to learn AS and keeps getting more advanced as he goes.
Humor: The easter eggs were kinda funny. Also, the crappy text on the title screens add a humorous overtone that probabaly wasn't intentional.
Overall: Even though this is a first game, and it's nothing we haven't seen before, it's decent. Average decent. Now watch fifty thousand tards release poor imitations of this already mediocre game, and we'll have to blam them all. Oh well. We'll burn that bridge while we're crossing it. You done good, kid. Now close the damn wad file and start making monsters out of Flash squares and triangles!
I look forward to your future submissions because this simple, short game didn't suck, and things will only get better as you grow.