It's ok
Your game has a really good concept, better than a lot of cannon related games that i've played. But to add some constructive criticism.. maybe if you made it so pressing the space bar after the character stops moving would being you straight back to the firing screen, rather than having to keep pulling the cursor onto the screen to click the retry button and then move it away because it obstructs the view, moving the mouse in and out of the box also makes the game lag on some computers..
also if you maybe had the cannon maintain its position from the last shot it made, I doubt anyones getting too far firing on the default 0 degree angle, having to readjust to a mid range angle after every shot gets annoying, especially after the last shot u made failed in a half second.
Having brought that up, i'll also add that staying in the air isn't as easy as it's made out to be, a bad ratio between helpful and un-helpful obstacles maybe? not that this part matters a whole lot. everything else is pretty good, like i said, it has a really good concept, also, kudos on having the smarts to change the weight and speed statistics of different characters, anyway, good job