very fun! a couple sound design suggestions:

•  try randomising the volume and pitch of the fire sound a little  each time it triggers, to vary it up a bit
• the fire sound ends quite abruptly at the end of the clip, so make sure it fades a bit nicer and for longer
• movement and collision sounds for the cannon, cannonballs and boxes are a great way to give a sense of real weight and material to the world
• for collisions, you can easily do it yourself and it'll be better than freesound - record some things of different materials falling off a table onto the floor. use audacity (free audio software) to change the speed and/or pitch of the sound until it feels right for the boxes. 

but it's got the makings of a good casual game, as others have said!

A simple game for a simple guy who loves to see the void, poetic

Looks legit. 

few more steps and it would be nice hypercasual game for apple/android.

SaTiSfAcTiOn OBTAINED

It was an interesting simulation of a sentient self moving cannon  I suppose. Maybe a guy wheeling around the cannon may have added to the realism. But I can't fault the actual physics interactions. Would be nice to have a voxel building generator to destroy or something.