Most time you've ever put into a game

[PxlStorm]

Pokemon Diamond (I think) with around 400h playtime on my first file. I've also restarted it several times, so it's likely around 500h. If Pearl and Platinum count towards it as well, it's around 600h.

Edit: I've also spent a lot of time playing Brawl and MK Double Dash. Probably 100-200h for each of them.