Alright game, quite simple and only 9 levels? (Not completely sure if there's another screen that unlocks after beating all 9, level 2 was quite difficult for me).
Suggestions:
Change of scenery each level. I've noticed level 1 and 2 have the same backdrop, and can assume the rest do too.
Give a reason to continue other than just unlocking levels. Maybe unlocking more guns or a grenade would be nice.
Make sure difficulty is paced. You go from needing to shoot twice in the first level to needing to have a firm strategy in the second level for the bullets to ricochet in the right way.
I've also noticed that after using your last bullet, you instantly lose. Even if you shoot your target.