It's not "very overrated" because nobody overrates it that way. The only time I've ever seen anyone claim that the Wii control scheme is supposed to be the best control scheme for everything is in Ian's posts. Everybody else realizes that, like every control scheme ever made, it has advantages and disadvantages.
Nintendo had the cajones to code name their console the "Revolution". That name didn't come across as Nintendo saying, "Our control scheme is going to have its advantages and disadvantages". It was hyperbole for sure, but it was Nintendo's hyperbole and nobody else's. So Nintendo overrated what they delivered - no surprise there.
I really like the Wii Remote, but it certainly hasn't changed the face of game control. It's proven to be a very viable, and even preferable, alternative for certain types of games (specifically, games that lend themselves to mimicking certain key motions, like the swinging of a bat or tossing of a bowling ball). However, it hasn't made everybody throw their joysticks in the ocean, which Nintendo seemed to infer leading up to Wii's release.
The Wii Remote/Nunchuk combo has always reminded me of one of those arcade games like DDR or Time Crisis. They have very specific hardware with very specific input mechanisms, meaning they're excellent for certain types of games. You could technically play any type of game on them by mapping normal controls to their proprietary input schemes, but you wouldn't necessarily want to.
I feel like the Wii Remote/Nunchuk is a good 1.0 version of the controller. I like where Nintendo's going with the idea, but the Wii controls just aren't mature enough yet to truly be considered revolutionary. And by revolutionary, I mean the "new standard" that's so good that joysticks go away entirely.