It is a simple, addictive, physics puzzle game. You have a cannon, and what you have to do is just aim and shoot at your enemy, i.e. a castle.
But here is the thing, it is not always just a simple target and fire scenario. Most of the time, a castle is behind walls and you have to make a perfect angle with walls so that when you fire your cannon, the cannonball will bounce through hurdles, exploding the enemy castle.