This is a great competitive game. There are basically three phases: castle building (wall placement), canon placement and combat. During the wall placement phase, you try to expand your castle using different shaped blocks, but you must be careful to completely surround an area during this phase or your game is over. During combat, the goal is to blast away your opponent's castle. (there are also ships to deal with in some scenarios).

TECH (real game - not emulated): The game came in two versions: a 2 player joystick version and a 3 player trackball version. The 2-player is standard JAMMA, but the 3-player is a custom interface. I have a 2-player board which the most finicky game I own with respect to voltage levels. Unless everything is perfect, it just resets over and over. I'm still looking for the 3-player version which is more fun..