Quick impressions:
Much better than Rock Revolution. The on-stage graphics, while not matching what is being played, are in 3D and move very well, as compared to Rock Revolution's static 2D clip art that moved from left to right occasionally.
Song choices? Varies between bubblegum pop and songs too emo-obscure for me to name. Having one of the better Hives songs on there was great and who doesn't love people attempting to sound like Michael Jackson?
The interface, at least for guitar, is the best I've played on DS in terms of guitar rhythm games. Notes come down and you have to touch them as they pass the fret bar. Nothing too complicated and it's fairly easy to play the game without hand cramps sitting regularly. The game on easy might be too easy, though, but I have a feeling this game is targeted to a younger (and based on all the pink and the fact that you choose created female avatars first, female) audience.
For those wanting a quick and easy Guitar Heroes game that can be played without the controller or a weird button config patch, this should kill some time at work or on a plane. However, only 15 songs total, so don't expect much.