Whether you started with a 2600 and a joystick in your hand, an N64 with a blistered palm or building your first PC in your teens, what is that one video game you've played at some point that to this day sits at the top of your list.
Tekken 3 for the sheer amount of times I beat it front to back. I had no memory card for my PS1 as a kid so I'd leave my Playstation on all weekend while I beat the game. Some days the power went out and I'd lose progress and have to beat it all over again.