There's nothing wrong with the controls. The problem may be YOU.
The problem starts with the tutorial mode. There, the monkey teaches you how to hold the remotes in order to hit the correct spots on screen. WRONG WRONG! The way that he tells is completely unaccurate and is the real issue behind the bad reviews.
For the correct position (please read carrefully that before playing), hold this way:
1- for middle circles, hold the Wii remotes horizontally, with the top of them (wit D-pads) pointing the sides of your body. Do not point them toward the TV screen or you'll have problems while shaking. This position is similar to the "lift the dumbbell" minigame from Wario Ware Smooth Moves and works exaclty the same way.
2- for upper circles, hold the remotes perpendiculary to your body, making its backs (with batteries) directly pointed to the TV screen. While shaking, do it toward the ceiling, not toward the TV screen, because the gravity attraction will work better on the accelerometers.
3- while hitting lower circles, just point the top of remotes to the ground. You don't have to point them directly to the floor, just keep a 45ยบ angle and shake normally.
After you're used to hold the remotes with both hands, you'll be able to proceed easily in the game. There are four difficulty levels (from Easy to Super Hard) and completing them will unlock all songs available in library (to quickplay or multiplayer fun). The new "Hustle Mode" (wich was included on ver. 2000 for DC) adds a few dancing movements to the music, and is way more enjoyable than the Original Mode (specially in multiplayer matches).
Wii's Samba de Amigo is probably one of the most underrated games of console history, and surely it's one of the best rhytm games of all time.