Worst idea ever? Basically taking Super Mario Bros and putting it in 3D for the first time ever, a bad idea? Mario Galaxy has its charm and will have its niche with fans, but it isn't the game everyone has been waiting for. I point to the success of the New Super Mario Bros on DS as my proof as to what type of Mario game people really want (even the first time it was shown, people gasped and cheered for the return of powerups and Luigi, as well as so much more). You need to look at the gameplay of Mario Kart, it is SMB with multiplayer in vehicles. You race to the end of a somewhat nonlinear themed track (shortcuts) gathering powerups along the way. Mario Bros is not about getting the shine or star or whatever other stupid RareWare type scavenger hunt they may half ass through in the future. Super Mario Bros was about a race to the end, it was the first game of capture the flag, and it never evolved beyond SMWorld in game design, until the DS (though the critics point out, no flying, and few new powerups). So why the hoopla over NSMB? Multiplayer, very simple. I have a lot of old games I think are great, but the games that every friend wants to play when they are here are SMB1, 2, and 3. The games set a standard for multiplayer from the beginning. People like to play together. And now it is time the series move fully into cooperative multiplayer, they have to 1up Halo, and remind the world, Nintendo stays at the forfront of multiplayer.
I would make Mario Kart on Wii a one handed game. The B button would be gas (I wish the button were analog so it could control simple, but tilting the remote forward would work like pressing the pedal further when holding B), A would be break (pulling the remote backward while hitting A would activate emergency break), you have the dpad for other mechanics like weapons. The motion control would control steering left and right by turning the remote. All the original Koopa kids, cell shading, new powerups, and level editor. Oh yeah, and plenty of online modes, optional microphone chat, before, during, and after the race, tournaments, ranked matches, etc.