In a recent interview in Famitu, Shigeru Miyamoto, Takao Shimizu, and Yoshiaki Koizumi revealed some tantalizing new details about Super Mario Galaxy.
Development of Super Mario Galaxy started when Yoshiaki Koizumi wanted to create a new game with the Tokyo Team. He took his idea to Mr. Miyamoto and they started working on the outline of the game. This happened right after the development of Donkey Kong Jungle Beat was finished. Mr. Miyamoto had been testing gravity effects even since the Nintendo 64, but the results were not satisfactory. It was until the Wii came along that it became something feasible. Super Mario Galaxy and Pikmin feature around 80% of all the ideas behind Mario 128. Nintendo may use the other 20% in about five years, but they'll remain secret until then.
Halfway through development, Mr. Miyamoto joined Mr. Koizumi as a co-director; he supervised many aspects of the game, from maps to physiscs, and made several suggestions to the team. Small spheric surfaces aren't really suited for a jumping game, so they gave Mario a new attack, the "spin movement," and created a method to fly from one planet to another, the "star rings."
Nintendo's new goal is to break the barrier separating hardcore and casual gamers. Mr. Miyamoto explains that there are both veteran and novice gamers working in the Super Mario Club, Nintendo's debugging team, and the novice members can catch up in just two weeks. In the days of the original Super Mario Bros., people would sit in front of the TV taking turns and having fun together. Thinking of that, the developers of Galaxy wanted to tear apart the new tendency of playing all alone, so they came up with the "assist play system," which they like to call "meddling play system." This system can either help the player controlling Mario or get in his way, depending on the second player's actions, so they'll have to communicate with one another if they want to reach a mutual understanding. Regarding the game difficulty, they wanted skilled and unskilled people to have fun. With the "assist play system," it's easier to get to a difficult place, while it can still be a challenge if you play it on your own.
As its title suggests, there are many planets in the game, maybe not enough to form a galaxy, but the planets from a single stage could certainly form a solar system.
Not having a free camera control is hard, since every player is different and wants to move the camera in many angles depending on the situation. This game features an intelligent camera system that makes the player forget about it.
Mr. Miyamoto stated that they'd like a simultaneous world release, but he hints at a possible release in Japan previous to the American one.