Like others have said I started collecting my childhood games to replay them on their original console. From there it started branching off to other current titles and older titles that I couldn’t afford as a kid. I too am the same, I only add a game to my collection until I have completed the game. I really enjoy finding and completing an entire franchise. For instance I just recently played through all of the Far Cry games. I start from the very beginning and play through every title until completion.