This is going to be a quick review as we've only played the game a few times. The real info comes in what I heard when the wife tried to start playing... You see, our daughter got High School Musical Sing It! for the Wii on her birthday (oh, yeah, we got a Wii over the holidays, yay!). She's a big fan of HSM, and a kindergartner, so we figured this would be a good match.
Sadly, the game makes having fun far too difficult. One of the best things about the Wii is the intuitive menu system. This sounds esoteric, but a complex device like a modern game machine actually requires finesse to make things "just work" without the usual screaming and frustration you'd find on your average PC. So when you go to do something, you find that it is really pretty easy to do, or it is obvious as to *what* you should do.
But HSM Sing It! completely drops the ball. I don't know if the geniuses at Disney Interactive were just lazy or mad or what, but I haven't seen an interface this frustrating since Windows ME. For example, we still can't figure out how to sing as a girl, so for a LONG time you'll have to sing as Troy. Because clearly 10-year-old boys are the target audience (!?!?!). And when you're in story mode, you'll be there for the forseeable future, as every time you try to bolt out of it, the game warns you: "ALL YOUR DATA WILL NOT BE SAVED." That's just bad game design-- let me save when I'm done with a song! In fact, the stuff you unlock is saved, but your progress isn't saved, which means you'll be singing the same several songs over and over and over again until the game decides it will smile upon you and finally save your data. Totally lame.
Worse still, the absolute basics are convoluted. We wound up naming our character "A" because that's all it would let us do. Menuing back and forth is like the world's most confusing corn maze. The gameplay is good, but not great, and you'll be wishing for a more complete playlist sooner than you think (would it have been so hard to include a couple of other Disney songs?).
Unless you're willing to slog through menus that make no sense, settings that don't stick and a very unforgiving save mechanism, this is really only for the hard-core HSM fan. Luckily my daughter IS such a creature, and thus far hasn't been completely disillusioned by the crappy game scheme outside the gameplay itself.