So a lot of fans are mixed on whether or not they want a Mario Galaxy 3... See the series has gone so cosmic that how could Mario possibly go back to the mushroom kingdom? While the style of the Galaxy series is without a doubt enjoyable, to base a complete new game on the same scene would be almost entering the same tedium as NSMB has.
So I propose a mass-kidnapping of epic proportions! You see, after helping her twice, Rosalina is visiting Mario and Peach in their humble Mushroom Kingdom. Whilst there, Bowser does his routine kidnapping of Peach, but while that happens Rosalina is also snatched, this time by Baby Bowser. It's up to Mario to save them. Daisy who's also dropped by to meet this much-talked-about Rosalina offers to help. But she's snagged by Tatanga (from Super Mario Land on the GB). So now there's three princesses to save. In fact since Tatanga is also supposed to be a space-creature maybe there's some link between him and Rosalina? I dunno just throwing that out there. Either way, by having three to save it could still create that sense of epicness whilst still keeping Mario ahem grounded. Any thoughts? Or would you be happy with a Mario Galaxy 3? If so or if not, then why?

Nintendo usually do well to not milk a specific idea for Mario Platformers.
SMB, SMB2, SMB3, SMW, SMW2, SMS, SM3DL were all very different from each other and all good games.
SMG had two games, but it felt like it offered good improvements.
So far the NSMB series is the only one they're milking, and to be honest I'd hate to see that continue, or to happen to SMG.
They need to make a new game altogether (Maybe a sequel to SM3DL, but even that'd be disappointingly lazy).

Looking forward to the next 3D Mario platformer but I'm bored of the Galaxy trope after two games. Honestly, even playing G2 it was feeling old for me.

I wouldn't mind a Galaxy 3 but I would want them to try something new

I'd prefer they didn't something new. After all, prior to Galaxy Nintendo never kept milking the same idea for two Mario games in a row, let alone three. Hence I'd want a brand new style of 3D Mario game for the Wii U, not just a Mario Galaxy sequel.

Wii U Mario will not be Galaxy 3.

I actually had an idea of one direction Nintendo could take their next 3D Mario...and that would be an open-world game.

I'm not talking about 'Grand Theft Mario'; but rather, an open-world game that is radically different to anything else - something that only Miyamoto and his pals could imagine up.

Just imagine a massive world that is essentially an out-of-this-world Mario playground, where 'levels' no longer exist; but instead are all melded together in a mass of mind-meting entertainment and gleeful experimentation. This open world would not only cover an immense area, but would also take advantage of the large vertical space that would come with it...a giant world that goes up and down, as well as left and right. In adittion, there would not be any artificial 'boarders' that stop the player in their tracks; no invisible walls to break the immersion. Maybe the whole thing could take place on a spherical planet? It would not be out of the realms of possibility to adopt such a construct from the Galaxy games...after all, Nintendo have adopted previous Mario mechanics for their sequels whilst creating new stuff.

Thoughts?

To be honest, I would prefer something linear. Like the early 2D Mario games, just in 3D. Kinda like the early Crash Bandicoot games or Rayman 2 and games like that.

Both Galaxy games were great (the sequel being the better of the two in my opinion) and if they feel like they still have more to offer in the Galaxy series, then I'd be happy for them to make a third.
If they feel like they've done everything they can with it, then it's time for something different.
Either way, I'm sure it'll be a top quality experience so I'll look forward to actually seeing it at E3.

Reminds me a bit of Banjo Tooie and Conker's Bad Fur Day, although even more open world in design. I kind of like it, especially given how much a Mario 64 and Sunshine fan I am.

Either you didn't read my post, or you haven't played any of the Mario games before Galaxy. Some examples please?

I'd love Galaxy 3, but I'd rather see a new series, and I'm sure most other people would too.

I like the idea of the open world, with radical changes of the enviroment during the run of the game depending on the actions.

I'm sure they'll do a new one. They seem like they're trying to take Zelda in a new direction for WiiU and I'd be surprised if they didn't do the same for 3D Mario.

I've already said this a bizzion times, but i think Mario's next step should be to enter the Dream World. Where else can you go after space? A proper '3D' spiritual follow up to SMB2 Doki Doki Panic would be totaly amazing. Miyamoto said he wants a sequal to happen but has held back since one of his buddy developers(Guessing the guy behind the NSMB series) Never worked with him on Doki Doki Panic/NSMB2. A little selfish maybe? Poor Miyamoto, considering SMB2 & 1 are his favorite in the franchise, or at least the most enjoyable that he's worked on.

I'd also like a completey 'new' 2D Mario with a new art style possibly made from clay or Wario land Shake it! toon style. The NSMB series needs to die already.

I'd prefer another original & innovative Mario game. Just like Galaxy was.

I like New Super Mario Bros. but I will agree that NSMBU should be their last one

Hopefully, it will be a non-linear platformer and have an open world like Super Mario 64.

That's what I'm hoping for, as well

I would rather have Sunshine 2.

I'd be in for a third Galazy title under one condition: make it less linear and disconnected. That was what I wanted the whole time I played the first two. Levels were so straightforward, while I just wanted to explore and mess with the gravity physics. The second interested me because of the addition of Yoshi in a 3D game yet the game felt even more linear. Let us explore galaxies freely, aim slingstars wherever we want and place planets close enough that we can jump between them and mess with the gravity between them! Open world galaxies. Give me that or just move on from the space theme.