I'm very excited about it. I think it's a pretty neat idea and looks like a ton of fun so far.
In SM64, the theme was "art" and "new worlds." It taught that you can enter new worlds through art, and that's exactly what Mario did. Subtly, too, it introduced the idea that video games (especially now when making the leap into the third dimension) are entering the realm of art. It was beautiful.
In Sunshine, the theme was "vacation." The world of Sunshine was that of relaxation, tropical adventure, and the idea that video games can be a form of healthy "escapism," much like an island vacation.
In Galaxy 1+2, the theme was "new horizons." The Wii, at the time, was Nintendo's attempt to innovate and expand what a video game was. Although, in retrospect, the Wii was little more than a wagglan gimmick, Galaxy 1+2, with the theme of new horizons, found Mario in space, planet hopping and traversing black holes.
In 3DWorld, the theme was "Nostalgia." Even though the linear, 3D playstyle was new (other than 3DLand), the idea was that one can only move forward by looking to the past. 3D World borrowed ideas from the original Mario games, and it was a great thing.
Odyssey looks like the theme is "Imagination." The realistic, New York Gray environment of what I imagine is the hub world grounds us in reality, and the Mad Hatter's hat (a la Lewis Carol's Alice in Wonderland) brings us into our imagination and colorful new horizons and shows us that gaming was invented for that very reason.
The hat gimmick looks super simple but extremely cool, too. Can't wait.