What does it take for a game to be universally enjoyable? That's the question most game developers would love to be able to answer, but it's easier said than done. My guess is that it comes down to exploiting the medium for what it does best -- utilizing multi-sensory connections to break down the barriers between the "real" world and the "game" world. If you look at the most popular game franchises in history -- Call of Duty, Wii Sports, Angry Birds, Guitar Hero, etc. -- you'll see that each one broke down those barriers in ways that deeply resonated with people on a primal level.
Will Rhythm Heaven Fever resonate with the populace at large in that way? I think it's possible. It definitely utilizes multi-sensory stimuli in ways that instantly make the player feel connected to the game world. It also comes packed with a kind of "Muppet cool" that historically appeals to kids, teenagers, adults, and just about everyone in between. It's way too strange and unconventional to ever come off as insincere or uninspired, and it's way too focused on blasting your brain with pure glee to be seen as anything but a whimsical delight.