This game is anything but "shallow".
The first thing people keep on saying is that this game is "shallow". It's completely untrue. Wii Music has over 60 instruments (most of which have to be unlocked). Over 50 Songs- each of which is divided into six parts (melody, harmony, percussion, etc)- each of which can be played with any of the 60+ instruments. On top of that, each song can be played in about a dozen different "styles" (electronic, rock, pop, Japanese, etc.). It's also worth noting that you can make your own styles. If that wasn't enough, you can change the tempo (ranging from really really slow to crazy fast). Oh, and most importantly, you can overdub. For example, you can play the drums to a song, then go back and play the bass, then go back and blah blah blah until you've recorded all the parts to the song. That's a lot right? I'm not done yet. The best part of Wii Music is that you're not tied down to playing only specific notes. Now, obviously, if you just go in and wave your arms like a monkey it's going to sound like crap. A surprising amount of skill is needed, believe it or not, to make it sound good. But you can add in your own little guitar/drum/cheerleader solos and truly make the song your own.
Another big complaint is that "it's just Rock Band for three year olds". If you think that, then you clearly don't understand what this game is about. Wii Music, as you might have noticed, is nothing like any music game out there. Rather than focusing on high scores and perfection, Wii Music is really about making music, and being creative. Wii Music is like the musical equivalent of LittleBigPlanet. Yeah, it's a music game, but it's really about customization and making the songs your own. For example, I'm really into doing orchestral renditions of songs and putting electronic beats (turntables, beatboxing, galactic drums) to them.
You thought I was done with depth didn't you? But I'm not. There's more. There's four basic ways to hold the controler. There's a position for playing drums and piano instruments, one for playing wind/brass instruments, one for playing guitar/bass, and one for playing string instruments. It sounds shallow, but every time I play I discover something new about each instrument. The reason people don't know about it is because the game doesn't tell you- you get to discover it on your own. There's 60+ instruments, but they each have their own individual qualities. I'm also surprised at the amount of people that don't know that you can turn the notes on when you play a song! Pressing the minus button while jamming will bring up the music notes (similar to guitar hero) so you know when to play. It says it at the top of the screen but some people couldn't figure that out! Sad.
My only complaint is in the mini-game department. There's a whole lot of quality but very little quantity. Mii Maestro (my favorite) has you conducting an orchestra. It's really addicting (esspecially with friends) but there's only five songs- a real downer. The same is true of Handbell Harmony- a great mini game. It's like guitar hero but with handbells. It's really challenging, but again there's only 5 songs. Shame. The other, and most challenging mini game is Pitch Perfect. It's sort of like a music themed WarioWare game. There's a lot more levels, but it's not as fun.
Bottom line: please give it a rent- at least. It may not appeal to everyone, but even if you don't think you'll like it, give it a try. It saddens me that sadistic self-indulgent fools like Game-Informer are turning people away from such a quality title.