Did you play the original Rhythm Tenega (Japanese GBA)? Rhythm Heaven? If so, buy this now. You're good to go.
For the rest of you: imagine WarioWare crossed with Guitar Hero, except the WarioWare minigames are longer (2-3 minutes instead of seconds) and there's no guitar. Rhythm Heaven Fever places you in control of a variety of wacky scenarios, from kicking soccer and footballs away from a pair of weasels on a date, matching the timing of a quintet of mile-high, square-headed tap dancers, and carefully screwing on the heads of robots in a factory.
The control scheme from the previous Rhythm Heaven games has been drastically simplified -- no waggle controls here. Rather, only the A and B buttons are used, with the majority of the games using only the A button on your Wii Remote. Sounds simple, right? The challenge lies in timing your presses to whatever inputs are on the screen and just plain getting the rhythm of the minigame down after multiple practice runs. For each given level, you can receive a "Try Again", a just "OK", and a "Superb". My kids are managing to get "OK" on most of the levels, but I can still challenge myself to earn "Superb" ratings on the minigames.
The bottom line is that this game is highly enjoyable and quite difficult. It's also longer than the original GBA game, if I recall correctly, but some favourites have returned (the square-headed tap dancers are reminiscent of the space dancers in the original, and Karate Man is back!). It's a fascinating and weird mix of genres that will have everybody in your family tapping their toes and singing along, "Yubayubadubadubayuba, is that true?" Great game and great value!