Sure, they were playing the Super Mario Bros. theme, and there were still some issues with the Wii remotes not always registering motion--an issue that was half-jokingly blamed on Wi-Fi interference--but there was some genuine improvisation during the song that made it seem like they were actually playing music, instead of playing with it. There were some instruments that, counter to every synthesized groan I've heard out of Wii Music so far, actually sounded good.
My newfound cautious optimism for Wii Music was rattled somewhat once I sat down with the game's drum controls afterwards. While much criticism has been leveled against Wii Music for a perceived lack of depth, the drums are a deep blue abyss compared to the other instruments, and I felt like I had been dropped in the middle of it. Between a Wii remote, nunchuk, and balance board, you've got a full drum kit sitting in front of you, something more full-featured and nuanced than anything I've seen from Rock Band 2 or Guitar Hero: World Tour. The controls are velocity sensitive, and the balance board actually requires you to use both of your feet.
The catch is that you also have to hold down buttons or analog sticks or directional pads to access most of the kit, and I'm totally secure in admitting that it requires way more coordination than I personally possess to make a good-sounding beat with these controls. My attempt to play a reggae version of La Bamba made for a combination not unlike bleach and ammonium. Additionally, Wii Music provides no cues for the drummer beyond the basic tempo of the song, leaving it up to the player to figure it out. It's an incredible amount of freedom, but it also seems at odds with Nintendo's whole mantra of expanded market accessibility.
I saw some of the potential for Wii Music, but I also saw some of its limitations as well. I'll be very curious to see how that expanded market responds when it hits store shelves later this month.