I have about 450 hours in Dark Souls.

I have three perfect saves in Final Fantasy Tactics, so that's many hundreds of hours right there. Getting all the buried treasures in Deep Dungeon by itself probably took hundreds of hours, not to mention getting every single character with every job skill maxed out. Cloud, especially, takes forever.

Fallout 3 and Fallout New Vegas also clock in at several hundred hours each, especially with mods. I'm sure I've spent tons of hours with Suikoden 1, 2, and 3, as well, getting all 108 characters.

I'm not even going to guess at WoW or Ragnarok Online.

For the most time to beat in one play through I would say Pokemon X and Y and Xenoblade at about 100 hours each, and for the most time played 300 hours for Fire Emblem Awakening.

The Elder Scrollers Oblivion!

Probably Chrono Cross and Final Fantasy VII.

Pokemon Diamond with 840 hours.

FF12 around 100 hours, FFx-2 international+last mission around 200+ hours, Kingdom hearts 2 around 100 hours, Pokemon silver around 250 hours.

Final Fantasy VII, because I missed the third Mystile so I played it again.

If MMO's count then WoW. If not > Oblivion.

Rings of Power on the Sega Megadrive, finished the game with out the walk through on the 1st playthrough, there isn't a game clock but guessing playtime was a couple of months