LUNAR LEEPERS / Sierra / Apple II
Lunar Leepers is basically Sierra's Defender clone, but it deserves a little better than to be written off that way. It was made by Richard Garriott (Lord British)'s college roommate, and actually takes the Defender concept and makes it a bit more complex. You're still rescuing doods that are waiting for pickup on the ground before the enemies get to them, but you're dealing with a basic Newtonian physics model that requires you to apply an equal and opposite amount of thrust to come to a stop over the peeps and land to pick them up. The Leepers are also a cooler enemy than anything in Defender; they jump to reach you, and if they catch you from the bottom they actually have a special animation where they pull your ship to the ground and chew it up.

It's initially easy to avoid the Leepers by sticking to the very top of the screen, but this strategy goes out the window when you're carrying a dude. Fuel is also a consideration; you don't have much and it has to be replenished at a little station that appears near the safe landing zone when you're low. Get through all that and you go into a second phase that's nothing like Defender - more like a traditional side-scrolling shooter where you have to navigate a cave full of traps and enemies to blow up the giant Leeper who rules them all or whatever.

It's a little kludgy to try to come back to and play today, but considering 1982 and Apple II and all that I think it's actually a pretty fun and inventive little twist on Defender.
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