The nunchuk control for the violin/cello is in a clunky position. Your wrist gets sore easily from twisting into its odd grip. You don't hold the violin - you hold the nunchuk. the violin just hangs off the side of the nunchuk mount. This mount comes loose easily during enthusiastic play, and the violin falls off.
The rest of the kit is a nice addition to your collection of Wii toys. They need to re-think the architecture of the violin, (and the guitar from the Wii Concert kit), but the horns, drumsticks, etc, are well worth the money.