OK been playing this, comes with a DS extension adapter so you can fit the grip on the OLD ds, but I use it so I can fit the grip on my DS Lite with the crystal/protector case on there..
First things first is that it's kind of awkward to press the buttons, you really need BIG hands to reach them, I think they should of used 3 buttons as 4 is too much, also after 30seoncds orso of playing your hands really start to ache..
Also the 3d graphics on the left screen are really Bad!!, but as your are concentrating on hitting the buttons and trying to push the pain in your hand away you don't really lpay attention to what's happening on the left screen apart form what buttons you need to hit..
The strumming is quite good as you can whammy on the touch screen at the same time, but you have to take your hand of the screen if you want to use the star power as you need to hit a/b/x/y or you can yell out but I doubt anyone would do that.... you don't really have time ot take yourhand off the touch screen though.
As for gameplay only tried quick play on normal I found I hit most of the notes, not bad, wish it had the guitar hero 3 songs though.... you have songs like All the Small things and Are you going ot be my girl which don't really suit it...
Will play some more and let you know my thoughts...
Was pretty gentle on the strokes though, you don't really need to put much force in them but I can see a lot of broken screens appearing...