In the newest Iwata Asks, Kirby producer Shigefumi Kawase revealed three Kirby games that never saw the light of day.
The first one is one that most of us know about. This was going to be a four-player coop adventure. It was originally planned for a GameCube release shortly after Kirby's Air Ride in 2003, but ended up being tossed away because of "how difficult it is to make a game that is both multi-player and single-player".
The next one was going to be a 3D open-world game that was going to have "extremely challenging gameplay". According to Kawase, it was scrapped because "we weren't able to achieve the quality we hoped for and it never reached completion".
The third games was a side-scrolling platformer made to look "sort of like a pop-up book", and was going to feature Copy Abilities, just like previous Kirby games.
All of these games were developed over the past eleven years, but were abandoned in the end in favor of Kirby's Return to Dreamland.
See the full interview here: http://iwataasks.nintendo.com/interviews/#/wii/kirby-dream-land/0/0