Speaking of handheld games...

I had this one when I was maybe ten or eleven that I traded away from a neighborhood kid. You controlled this missile launcher at the bottom of the screen with a knob that moved it left and right and a button that sent your missile shooting straight up towards the top of the screen.

Enemy aircraft crossed from left to right at different speeds and altitudes. When it died, I cracked it open and was fascinated to see that it was entirely electromechanical: Each flight level of aircraft was a filmstrip that scrolled in a continuous loop. Your missile ran on a vertical track; the "reload" time was how long it took to get the little backlit plastic missile back down to the bottom of the screen.

Given all the monkey motion going on inside that little plastic case, it's a wonder that it survived as long as it did in my hands.