Super Mario Galaxy was a great game, and I put it up there as the best platformer I've ever played next to (if we aren't including Mario titles) Psychonauts. The concept is beautiful, the game was beautiful, the physics were beautiful, everything about that game was gorgeous.
Of course, then came along Super Mario Galaxy 2. It was also an extremely gorgeous game, but my question is "Did it really justify a $50 purchase (assuming you got it new) if you adored the first game to death?" My answer would probably be no. It was still very exciting to play, but it felt very similar to the first game, maybe even different in a little bit of a bad way. Unlike the first game, which was designed specifically with a celestial feel (hence the galaxy part), Super Mario Galaxy 2 felt very flat, almost like Super Mario 3D Land (I haven't played the title, so I can't judge). So, a Super Mario Galaxy 3 would leave me a bit uneasy.
Now, if Nintendo was to make Super Mario Galaxy 3 more celestial than just have platforms randomly placed that you can warp to, then I'll be the happy camper I was with the first title. ^^
I wouldn't like to see another Galaxy game on the WiiU, every generation has brought us new mario experiences and i dont want the WiiU to stray form that considering its nintendo's first HD console, Mario 64 and Mario Sunshine were very solid and appealing installments but we never got sequels to them, yet we did for Galaxy and even though Galaxy 2 was primarily the ideas left out of number one, particularly the inclusion of Yoshi, i dont think it'd be wise to see the same game again... perhaps for the 3DS a version of mario galaxy could be a reality but for a mainstage such as a home HD console, the next Mario game, much like Zelda, needs a gameplay design and mechanic and theme that really shows off what the console can do and i dont think mario galaxy could do that without getting a backlash for being repetitive from critics and in all probability, the fans who want it.