Even though it is being developed by the Mario Galaxy team, this game is more like a New Mario Bros game in 3D. Levels will have an end-stage flag and 3 star coins. It seems like no star collecting will be present, which is a first for a 3D Mario platformer. I'm not complaining, it's interesting, but it will feel different [edit: ... without stars].
There is a new Iwata asks video were he asks Miamoto-san about the concept for the game. Miamoto-san said he developed the game to be 3D in it's graphic style, but to play more like a 2D Mario. He said players will find the main game fairly easy until about world 8 if they just go straight through, but he said there are a lot of optional things to do and secrets to find.
This game will be so great. I know people always complain about Nintendo relying too much on their franchises, but what company doesn't? And besides, Mario games always have a ridiculous level of polish and charm that is only matched by kittens with rainbows shooting out of their eyes as you watch while you lay on a cloud that you just woke up on.