You're kind of saying that casuals are people who hate to lose, and can't stand doing something wrong. I think that this game seems great, but I haven't played it yet, so I'll have to skip the quality part.
For sales, this title could easily sell 400K by the end of the year in Japan. It launched in the most dead time of the year, and overall, its sales are respectable.
Console music games do not sell in Japan. No console music game has, to my knowledge, sold 100K in Japan. Are you calling a game that is likely to sell at least 5 times of that a failure there? Nope. Wii Music greatly expanded the console music genre in Japan.
As for America, it doesn't seem like it will take off, but I have faith that it can make 1M there. It should WW manage to sell 2M by the end of the year, which is by no means bad.
http://www.vgchartz.com/games/userreviewdisp.php?id=261
That is VGChartz LONGEST review. And it's NOT Cute Kitten DS
