Critical-Gaming Network

Good core music-rhythm design: SHAKE, RAPID SHAKES, POSE, DANCE. Between these mechanics, the various rhythm patterns, and the 6 shaking zones Samba De Amigo can create more significant variation than most music-rhythm games.
For single notes, the player can perform a "trick shot" by shaking the two "maracas" in the same position at the same time. This option gives players a way to increase the difficulty of relatively simple sections while scoring more points in the process.
The core design is very similar to the Elite Beat Agents/the Ouendan series for the Nintendo DS. Shakes = TAPS. POSE = DRAG. DANCE = SPIN (where players can put more energy in to this mechanic to earn more points). Furthermore, the game is designed around creating an interactive sound scape of percussion as opposed to an interactive music track like in Guitar Hero. In Samba De Amigo, players aren't making music. Rather, players shake and dance to the beat.
Not enough negative feedback. When a player shakes at the right time but accidentally slips into the wrong position it feels like the game simply didn't receive the SHAKE input when in fact it did. The game only Boo's when your rank drops a letter grade. Otherwise, it's very hard to tell whether the game really missed the input, you didn't SHAKE in the correct zone, or if you just didn't time it right.
There's no penalty for shaking in the times/spaces between notes. Because playing Samba De Amigo involves a lot of movement, it would be frustrating if the game penalized players for every SHAKE that wasn't timed to a note. Often times, I found myself shaking both hands to keep the beat even though only one was necessary. This design decision is key to keeping the game focused considering the nature of the game and the controller input in addition to allowing the player to "free style" developing their own subdivisions as they sync with the rhythm of a song.
The rating system is very old school Japanese with a few convoluted quirks. Unlike Guitar Hero (a Western music-rhythm game) where players receive full credit for a note as long as they hit it within the timing window, in Samba De Amigo playing exactly on the beat is privileged. Landing close to the beat will award the player with points, but only by landing perfectly on beat will the player receive full points while increasing the multiplier. In traditional Japanese music-rhythm games, the developers just don't want you to play, they want you to play perfectly.
On top of the percentage grade based on correct notes played, in Samba De Amigo, Ouendan, and DDR, a letter grade is given as well. On top of this, the letter grade in Samba De Amigo doesn't directly correspond to the percentage of the correct notes played. I once got a score of 96% and ended up with a C rating. While playing players not only build up their multiplier and score, but a meter that determines their letter grade as well. With a few mistakes, the later grade drops. With much correct playing, the letter grade slowly climbs. Though this system is unnecessarily complicated everyone knows how to improve their score in a music-rhythm game. Play all perfect notes without missing one. Do that, and understanding the scoring system won't matter.
The mini games aren't worth the time or the money Gearbox spent making them. They reminded me of some of Boom Blox's worst mini games... distractions from the core design of the game that should be avoided.
The option to play with Wiimote + Nunchuck or double Wiimotes is much appreciated. The calibration options seem to help as well.

The tri-colored zone display isn't intuitive for those of us who have gotten used to reading music on a linear "tape reel" type system. Sheet Music, Guitar Hero, Donkey Konga, and even Ouendan have a very linear structure to their notation. In Samba De Amigo, the notes spawn and branch out from the center of the display. While this design may be counter intuitive in one regard, it's great for indicating the spatial relationship the notes have to where the player must SHAKE. I found that when I lost track of all the moving dots, I could still hit all of the notes fairly easily by maintaining a soft focus on the colorful display. The effectiveness of this design is also evident when the POSE/DANCE sections come up. Without thinking, I was able to successfully mirror the position indicated on the screen.
Being forced to play through the Normal and then Hard campaign to unlock the Super Hard mode was slightly irritating. I didn't realize how much I've gotten used to the Western design for music-rhythm games thanks to Guitar Hero. I expected that all the difficulty modes would be unlocked. Over all, unlocking songs and modes in Samba De Amigo isn't a big deal.

There are many nuances and techniques to playing Samba De Amigo that differ with each song just like there is in any quality music-rhythm game. If you don't spend the time to learn it, you shouldn't fault the game. Many claim that the controls simply aren't accurate enough. In my experience, the Nunchuck works best on the normal difficulty. Clearly, playing with two Wiimotes is ideal. They're more accurate. They have a longer grip. And there isn't a cord hanging between them, which frees the arms for pulling off a double "around the world" dance maneuver. I've score 90+% sight reading Hard mode and about 85+% sight reading Super Hard. If I spend the time to work on a few techniques I'm sure I can ace any of the songs.

Samba De Amigo is a game that I feel would have benefited the most from implementing Wii Motion Plus technology. The current way the game figures out what positions the Wiimotes are in (high, mid, low) is jittery and finicky. If a sequel comes out with Motion Plus controls and maybe even some Balance Board support, I'll be the first in line.