I haven't got the slightest clue about my super young years, which I replayed the same games over and over.
But past 2000s, I probably played Halo 2 the most. We would rent this game every month or so and play through the campaign every time. Eventually I even beat it on Legendary.
Another relatively short but enjoyable experience was the Spyro trilogy, especially the first one since it is oldest. And each time I had the knack to play any of the Spyros, I had to beat Spyro the Dragon first.
Digimon World was beaten multiple times, as well as Pokemon Yellow.
For longer games, FFX is the winner. Multiple times played through despite the length of the game.