Pokemon Ruby. If I remembered correctly, I had amassed 187 hours of gameplay in only two years, and then Emerald was released, and I had like 150 hours of gameplay over two years, and then Diamond was released...I had a lot of free time when I was a child.
Hmm, I played Grand Theft Auto: San Andreas the longest. From when it was released and up to this day I still play it.
It's one of the best games I've ever seen, one of my favorites. The graphics suck and there's a lot of glitches but who cares with that story and gameplay?
Rayman 2 the great escape on ps1. It isn't a particularly long or difficult game only when I played it I knew nothing about videogames, I was a huge noob.