At the easiest level of play the notes don't come down any more often that once per beat with the occasional 8th note scrolling past. At the highest levels there is about a one to one correspondence between the dots you see and the notes in the lead guitar line of the song that is playing.
Will playing guitar teach you how to actually play guitar? No. Will it teach you to read music? No. Does it have some value? It just might. The whole game is set to rock music. You need good rhythmic skills to listen to the music, follow the dots, and "play" the notes at the right time.
That's great if you like heavy metal, but what about the rest of us. We are band geeks after all, and probably have interests in music that lie outside of (or perhaps for some of us overlapping) the heavy metal genre. I propose that these software developers come up with a game with a more classical flavor: Conductor Hero III: Legends of the Concert Hall. The controller could be a novelty sized baton into which the Wii controller fits. Then the "conductor" could respond by gesturing with his baton to visual cues on the screen all while classical music plays.
Perhaps this game idea wouldn't have as big of a popular appeal as the Legends of Rock, but we band geeks can still dream!