I don't understand how 3D isn't a gimmick when the whole game revolves around it. Super Mario 64 was built entirely around the idea of it being a 3D platform, and by your owne definition of a gimmick, that makes the 3D aspect of it a gimmick.
Editing to add: I don't know if nostalgia is their gimmick, really. I mean, that's really defensable that it is. I can see where you're coming from. But I don't know if that's Nintendo intentionally cashing in on a nostalgic audience, or if it's Nintendo attempting to emulate what they saw as their heyday. I do agree, though, that Nintendo is crushing their own franchises.
Editing to add: I don't know if nostalgia is their gimmick, really. I mean, that's really defensable that it is. I can see where you're coming from. But I don't know if that's Nintendo intentionally cashing in on a nostalgic audience, or if it's Nintendo attempting to emulate what they saw as their heyday. I do agree, though, that Nintendo is crushing their own franchises.