Nicely put together. The controls are smooth, and the primary gameplay loop works well!
The game might have been a little more challenging if the timing of the two cannons was not identical. That way, you have to dodge one, then the other.
When it comes to the color scheme, the player character blends in a lot with the background. Of course this isn't a huge problem once the player begins to move, but in general you want your player character to look distinctive against the background.
There are a couple of elements that probably go against the jam rules: the way the cannons rotate freely is not in keeping with the 160x144 resolution rule, and the need to click "Start" with the mouse is not in keeping with the Gameboy controls (there might have been another way to start the game, but in that case I just couldn't figure it out! :) ).