Laser cutters are inherently fun (the clue's in the name), so connecting one up to a webcam so you can play Space Invaders on it is only going to do good things.
The set-up uses a very slightly modified Whitetooth A1 machine with an 80W laser tube and a webcam to provide the game's more familiar view-point. The player then controls the laser cutter's head, moving and firing it to destroy the very flammable invaders via a PC. Those are mounted on the cutters internal workings, which already does the up and down bit, with an extra motor added for some left and right. The arrangement even has foam 'shields' that you make holes in to shoot though.
[Space Invaders made real! = Just Add Sharks]
[How NOT to play space invaders: with a laser-cutter - Slash Gear]