I'm already at 300 hours on Pokemon X. I've owned every single generation and remake, and I should've played for at least one hour each. So about 2k hours throughout all of Pokemon X-X

Metal Gear Solid Peace Walker. Probably like 300 hours. And other 200 hours on an old save I deleted by accident.

I'm pretty sure halo 2 would be at least 2500 hours for me. Other series around 1000 hours are pokemon red/blue, thps, Mario kart. I already have over 150 hours on mk8.

WoW, Oblivion, Left 4 Dead 2, Kingdom Hearts and Civilization V are my top 5.

Runescape. I've been playing it since like 2005, stopped between 2009 to 2011 then got back on it. It's just that one game I can't seem to get over. Lore is actually really interested and it has some of the best quests on any MMO in my opinion, mainly because they aren't used just to substitute grinding (or kill 200 something boars) but rather tell stories and boss battles.

Close seconds are MapleStory and League of Legends.

Non-MMO, it would have to be the Dissidia Final Fantasy spin-offs. So much fun on the go.

probably okami. or super smash bros brawl. or maybe super mario world and the donkey kong country trilogy

FF7 - Farming sources to max all of Cloud's stats at 255 and partly for Tifa.
FFX - Maxing everyone's sphere grids, beating the 10mill hp boss and lots of blitzball.
WoW - Played for 5 years after release.
Dragon's Dogma - Played through it again after losing my save file. Farmed alot of the highest gear during the first playthrough then again in Dark Arisen.

Call of Duty Black Ops : I had like 34 days played in that game ( I know, no life )

Put close to 4000 hours into Starcraft brood war, next after that would be in the hundreds, maybe civ2

I spent my childhood in Mario Kart: Double Dash!!

Otherwise, it ought to be GTA Vice City Stories.
It's just fun to shoot people, you know?