The interface is a critical part of the game. Nobody plays DDR with a hand controller. Guitar Hero wouldn't be the phenomenon it is without that plastic guitar. Just as you cannot play badminton without rackets, shuttles, and a net, you cannot play Wii Fit without a board. The so-called "peripheral" is an integral part of the game itself. Trying to seperate the game from the interface is like trying to take a train off its tracks: Everything just stops working.
In previous generations, very few games successfully broke out of the default gamepad interface. Maybe it was the price, or more limited technology (wires in the living room are annoying) or lukewarm software support. Maybe the market simply found video games themselves to be enough of a novelty that they didn't need to push things with new interfaces.
Now, after a couple decades of limiting interface to the gamepad, game designers are breaking away from merely evolving the gamepad and the gameplay mechanics that rely on it. They're introducing new interfaces to develop new game mechanics. And people are excited by new experiences. Maybe these new interfaces are getting the serious support they need to succeed. Or maybe the market was just tired of the gamepad and longing for something fresh.
"The worst part about these reviews is they are [subjective]--and their scores often depend on how drunk you got the media at a Street Fighter event." — Mona Hamilton, Capcom Senior VP of Marketing
*Image indefinitely borrowed from BrainBoxLtd without his consent.
