I'll just go ahead and list...
Pokémon Diamond, Pearl, and Platinum - All of these games combined, I must have anywhere between 400-900 hours on them. I love the
Pokémon franchise with all of my heart, and those three games were some of my favorites. It's a shame that I've lost the cartridges, otherwise I would have a more definite time to post.
Animal Crossing (GC, DS, Wii, 3DS) - I've played all of the
Animal Crossing games, each with varying hours on them. As of right now, I've spent the most time playing
Wild World. It was my first official
Animal Crossing game, and I nearly played it everyday ever since I got it. I didn't bother much with the original game and City Folk, mainly because they didn't spark my interest like WW did. Then
New Leaf was released, and as of this post, I have logged in 110 hours and 23 minutes on it. I plan to spend much, much more time on it.
Ocarina of Time - I've spent about 81 hours on
Ocarina of Time, as I found the game extremely entertaining. I've must've replayed it over 10 times by now, maybe even 20. I've lost count!
Super Smash Bros. (Melee and Brawl) - Between the GameCube and Wii releases in the
Smash Bros. series, I'd have to estimate that I've logged in over 100 hours on both combined; however, I've spent more time on
Melee than I ever did on
Brawl.
Sonic Adventure 2 Battle - I have spent so much time playing this game that I can't even estimate any numbers. I've played multiplayer and single so many times that the disc is completely full of scratches. D: Love comes with a price, I guess...
Sonic Adventure DX: Directors Cut - I really liked this game, and as such I've compiled a lot of hours on it. If I had to go ahead and guess, I'd estimate at around 30-60 hours. It's a fun game, and I'd recommend it to everyone here!