Panzer Dragoon for the Saturn - more than 100 hours. It couldn't afford a game back then so the demo disk on the Saturn was the only thing I could play for more than half a year. Panzer Dragoon sticks out as the best of the bunch and help me purchase the game at a later date.
Current gen: GT5 Time trail, spent a lot of time with friends trying to beat each other time, I suck at this and almost always come last. Didn't play it by myself but 20-30hrs for sure.