In terms of time spent, there's a fair amount:
Final Fantasy VII: Got it Christmas '98. Must've done at least five playthroughs before we got a PS2. Revisited it once or twice during that era. Replayed it once that I can think of in 2010. Just finished a platinum playthrough on PS4 earlier this year (which felt very strange). Even being generous and saying none of those saves went over 40 hours, that's still... 360 or so hours?!
Final Fantasy X: My original save on PS2 was well over 100 hours, and that was in addition to a secondary when I realized I had messed up getting a final weapon. I got the PS3 remaster years ago and it's sitting at around the same amount of time, though in both cases, there's a good chance it was left running when I wasn't actually playing.
Gran Turismo 4: I think this ends up ahead of GT3, largely because of Photomode and the community here. I slowly phased it out around late 2008 or so — and gaming in general, for a short while — but the size of it is what kept me playing.
Super Mario Brothers 3: The classic. I couldn't tell you how many times I've played this, from the age of about four to as recently as a few weeks ago. It never gets old to me. It's just an enjoyable title that has outstanding depth given the entire game is less data than a decently-sized image these days.
Sonic the Hedgehog 2: The best Sonic game. We were a Genesis household in a sea of SNES places as a kid, and while I love me some SML, Sonic 2 was just more my style back then. The speed, the fluidity — this game is etched in my mind. My sister and I played through it last year, and we
still knew every little secret and grabbed all the emeralds by the end of the Chemical Plant.
Jet Moto: The odd one out in this group, I'll admit. This wasn't a fantastic game, but it was the source of hours of entertainment in our neighbourhood. When a few friends and I stumbled across our own version of Tag in Jet Moto, that became the name of the game. Basically, you started a head-to-head race, and whoever made it to the Rocks section in the map below last was "it". With the various cheats in the game, it was possible to climb the huge lower left rock, or launch off it for seconds of air time. So much fun.
Metal Gear Solid 2: Collecting dog tags. Trying to make sense of the story. Teenage Slip
loved this stuff.
Grand Theft Auto San Andreas: The sheer scale of this game was just amazing back in the early aughts. I'd load it up just to cruise, or explore. It's something I find appealing about GTAV, but being much older, the opportunities are few and far between.