It's a fun and addictive game, great for a party, even though it has some frustrating issues...
Compared to the Dreamcast version which calculates the height of the maracas with ultrasonics, this version uses only the maracas' angle. Sometimes if you don't position the Wii Remotes correctly enough for the game's likes, the game will find it difficult to choose which move you were actually doing. And sometimes a few maracas hits will mysteriously not be detected or will be detected as maracas position changes or vice-versa. This happens a lot with the Nunchuk but also when you choose to play with two Wii Remotes. Yes, you can play alone with a Wii Remote on each hands, which is kind of awesome since it has never been done before (correct me if I'm wrong).
Most of the music soundtracks on Dreamcast (including the 2k version) are also on Wii but have been remade nicely. I personally prefer 'Samba de Janeiro' on Wii than on Dreamcast. The differences aren't major though.
Also, the Stereo sound on Dreamcast versus Dolby Digital sound quality on Wii makes that game a little more enjoyable for the ears than its predecessor.
You can unlock in the new Career Mode a bunch of funny sounds (even cute Chao sounds) for your maracas, a load of nice soundtracks and even making-of videos. Beware Sonic/Sega fans, not a single Sega game soundtrack that was available on the Dreamcast is on the Wii.
There's a download section where you can buy packs of songs for the game (and it doesn't worth it for 500 Wii points each). On the Dreamcast, you could unlock a good number of Sega game soundtracks such as 'Let Mom Sleep' or 'Open Your Heart' on the Internet for free. Unlike the Wii packs of songs, the Dreamcast game had already these songs hidden on the GD-Rom, so buying and downloading the Wii packs takes memory on your Wii console.
There are good sides and bad sides. It's up to you to decide if it's worth buying it. If you want to listen to sunny and joyful Latin music while flailing crazily your arms (you know you want to), I recommend Samba de Amigo for you and for bringing it at a party.