Guitar Hero is going to be the best selling 3rd party franchise this generation. As a matter of fact, I believe that only the Wii franchise can beat it if you call Mario Party and Mario Kart (etc) different franchises.
Well, top 3 in best selling franchises this gen is my guess(including first parties) and top 5 should be a guarantee.
BTW, this is also comming to Ps2, is it likely to be damaged because of that, or are Activision not doing bad ports from Ps2?
http://www.vgchartz.com/games/userreviewdisp.php?id=261
That is VGChartz LONGEST review. And it's NOT Cute Kitten DS