Good, but not great.
The graphics could've been better, but they weren't horrible. The gameplay was very repetitive, and it took much too long to increase in difficulty significantly. On level 13, for some reason no enemies came, and I just had to quit. Every time you upgrade the reloading speed, it says you don't have enough money, even though it still upgrades it.
Also, after you kill an enemy, if you keep shooting you will gain points for a short while. in this way, when I'm supposed to kill 10 enemies, I can get away with killing only 3. When the screen is "opening," it doesn't show all the upgrades you have, and if there i an enemy when it's "closing," it will show over the closing screen.
Another thing that bugged me a bit was how the cursor went under most of the things on the screen. Also, you should put labels next to the bars so people understand what they are immediately. It took me a while to figure it out.
I know, this seems like a lot. But hey, I played up to level 13. This game was still sort of addicting!
Keep trying. You're not too bad. ;)