I beat Pokémon XD in a day, but that's because I was borrowing it from a friend who also wouldn't lend me his memory card, and since I was playing on a Wii it couldn't save normally. I spent the whole 24 hours playing and I was speeding through it but it was still a ton of fun for me!
A lot of Kirby games can be beaten quick, but besides Return to Dreamland, I don't think I've beaten and in a day, but to be fair I haven't wanted to. Most times, I limit myself to only playing an hour on the first day, and then going as much as I want the second day just to at least make it last a bit longer. Doesn't increase the time by much, but it increases it by enough.