Nice game! Very good sprites, nice music, and shooting around feels very good. The game screen is a little too big, the level transition is a little sudden and there are some minor bugs like double jumping using W and Space. Also, I think the controls could use a little tuning to make them work better for the kind of precision platforming the first level has
All around I think you nailed the theme and had very creative ideas, like on the second level having to jump around with the cannon.