Not bad.
The basis for this game I thought was pretty good, though seemingly unoriginal...
I think that it needs some improving though, you really need some gun sound effects in there or something to add to this, it was really quite bland all and all, unfortunately.
There appears to be a bug in the game, where the score doesn't reset between games.... a definate drawback, and an impact on the score.
I think that it could also use some sort of ammo limit too, this way... it's too easy....
Needs to be more challenging.