The problem isn't just innovation or lack thereof, it's the sense that the franchise's prestige is being slowly sacrificed in favor of its sales potential. There's something that feels very desperate with the manner in which Mario is being deployed the last several years.
And, yeah, the game isn't mindblowing. And that is sort of a big deal. I understand that you made the "nostalgia" argument, that these games will never excite us in a way they did when we were kids, but I respectfully disagree. I grew up with SMB3, World, and 64... Iremember these games vividly. And you know what? Galaxy managed to tap into that childlike feeling of wonder as well as any of those three did.
Since then, it feels like the Mario series has been cynically turned into a cash cow. Which, from a business standpoint, makes perfect financial sense. And it's not like the quality of these games have suffered. But there's a certain freshness and excitement that's been missing from Mario the last five or so years, where it feels like we're just going through the motions.