We have had two Mario Galaxy games featuring floating 3D lands... and they have been awesome. Now we have Mario 3D Land on the 3DS, essentially more of the same but still a solid game.
I wonder what Nintendo will do next with the plumber. I feel like more of the same might just become boring and predictable. Something the media have started to complain about in relation to their IP. Sure they can introduce more power ups, or suits, invent some interesting obstacles but I hope they can find something beyond that to really shake things up a bit from the current formula.
They did release New Super Mario Bros. which was interesting. I guess we will have another instalment of that at some point given its popularity.
Personally, but this might be the retro-head in me, I would love them to go back to the pixel art presentation for one game. Perhaps apply some gorgeous multi-layered pixel art style to the next instalment of New Super Mario Bros. (I miss playing MArio World!).
Then of course, what about a return to the world of sleep we visited in Super Mario Bros. 2?...
I'd love to see Nintendo take a bit of a risk with Mario, but they haven't looked like doing it for quite some time. Perhaps that'll change now that their hold on the handheld market is wavering and people are burnt out on the Wii.
I think there are always two versions of one Mario type of game:
NES: Super Mario Bros. 1+2 (JAP), the non-JAP Version of Mario 2 isn't really a Mario game so I don't count that) are quite the same, Mario 3 was quite new.
SNES: Super Mario World seems to me like an updated Mario 3, with new Ideas like Yoshi etc.
SMW2 (Yoshi's Island) well, it's not really a Mario game is it?
N64: Mario 64, completly new stuff in 3D and all, a Mario 64 2 was planned but was finished
GCN: Sunshine, again completly new with all the water stuff, the GCN wasn't that popular so they might have a Sunshine 2 in the works but scraped it because of that?
Wii: Galaxy, and again completly new with all the planets stuff, Galaxy 2 is of course an updated version
I don't know much about handhelds, so I can't say what they did there.
I think the Wii U will get something completly new again, no Galaxy stuff anymore. And I don't think that they will do something SMB2 (non-Jap) related.