Great game
I feel as though this could be a really cool speed game though there were a few things I noticed.
1) As a lot of comments already say a key that would make the cannon ball come back would be great.
2) The ball comes out of the tip of the cannon allowing it to shoot through walls if positioned correctly, I don't know if this is a bug but it could definitely be used for some interesting level design such as hitting a target or button through a wall allowing the user to pass.
3) An in game timer would be awesome.
4) I noticed when playing through that if falling fast enough and shooting downwards you could hit yourself before the cannon ball bounced of anything which would give you a little height and stall you a bit this could also be super cool level design.
5) Like the bombs another chain reaction block would be cool but the user could touch it without dying.
6) The idea of sinc jumping is cool makes it feel like rocket jumping in tf2 however the explosions would suck you in and not blast you away if this is unintended it is probably because the hit box on the other side of the explosion is trying to blast you that way.
7) Extra bouncy blocks.
I know this was a long paragraph but if you wanted to make it a bigger game than this is what I personally would like to see changed or added to not take this as criticism I loved playing though this game. In case you are unaware of tf2 or rocket jumping I have included a video bellow. Thanks!