So as of now, most Gamestops will have a store copy of Guitar Hero for the DS that you can play. I got my hands on one and was playing it for 2 straight hours when I was suppose to be working. It's really fun, just as addicting as the bigger brother console versions. The songs are pretty good but I don't think the soundtrack compares to the console versions. The 'guitar' add on seems pretty weird at first but it actually plays quite comfortably.
The way you hit the notes can be aggravating at times until you get used to it - like the 360 or PS3 guitar, you hold down the color of the note, but unlike the console version, you use your stylus to strum the guitar on the touch screen. To get star power you can either scream into your DS

, or press pretty much any button on the hand held

.
Overall, it plays like the other Guitar Hero's when you finally get the feel of it. If you have a DS and are looking for a good game to add to your collection and your a Guitar Hero fan, I highly suggest this game.