Computer - Radar Rat Race on the C-64, bought it in cartridge when I got the computer just to have something to start with. Last cartridge game I bought too, the rest were either on tape, later floppy disk, or typed in from a computer magazine. On the latter, I think they were trying to develop a generation of programmers with those and intentionally put bugs in them to make them not work until you fixed them. Every one.
Arcade - that's a harder one to remember, but I do know it/they would have been at a roller skating rink. Probably Asteroids as that would have gotten my attention first, or Turbo or Wizard of Wor.
Still worth it, one of the best games, especially if you had a good joystick (Kraft). The amazing part about that game is how the movement "felt" fluid even though it was just a digital thing. I can't describe it, but I think anyone who played it understands how it felt analog in its play, how you could jump and tap just so and do amazing moves.