Like dsmith said, the power of the cannon needs to be more effective. I can't fire at the maximum range much at all. It'd be nice if I could alter the power as well with say the arrow keys, and simply change the angle with the mouse.
Aesthetically, the artwork looks nice, but I'd like for the different ammos to have a different color. Not necessarily the barrels though, as I'm certain this game does try to make the player use his/her math skills (even if its basic).
It'd be nice to have all the ammos mapped to 1-0, so I could change them without having to click it. And add a 10 and 100 type ammo.
Besides that, no complaints. It is what it is, and I like that it doesn't try to claim it's more. :) 3.5/5