Pretty good =)
This game is pretty fun !
The good points are that the graphics are very good, it looks like there has been a hard work on the details of the drawings !
Also, the physics research are fun.
The way to use the cannon is easy to hand, which is a very good point !
Although, I see some black spots : It's too bad that the monsters are so static when they get attacked or die. Maybe you should have done an animation for that !
It also seems that under Newgrounds, the game doesn't fit the window. I think we can't see everything on the corners.
And last but not least, the thing is that I don't like seeing too much advertisement, and the fact that you give a link to one of your other game every time a level ends up cuts the possibility to be really into the game... I can't possibly blame you for that, but, you know...
Anyway. That's just an opinion, take it as you like =)