Nice!
Not bad, not bad at all!
Sound, graphics and effects are nice, but you might wanna work on the spelling and the speech bubble. Also, the boss was kinda...too strong in my opinion, with the low HP I had left in the end.
Also, it would be better if you could choose to shoot one target twice, so yes, to be able to pick your target manually would be nice.
Anyway, good job! If you made a whole game out of it I'd definitely play it. Also good soundtrack, nothing too boring or so.