Rodney McAuley's Wavy Navy is arguably the best Galaxian clone that was made. You control a boat that has to shoot down diving planes and helicopters but things are complicated by the fact that you have to move back and forth over a ridiculously undulating sealine. Stuff comes at you from below the water sometimes and you often have to time your movements in accordance with the movement of the waves to avoid what's coming at you. I like Galaxian as well as the next person, but I like Wavy Navy even more (preferably the Apple II version).
