Most reviewers are hardcore gamers (many of them biased towards platforms, IMO US reviewers mostly to the advantage of the 360).
I can easily understand why "party games" are so popular, but I can understand why hardcore gamers can be bored quickly and compare graphics, complexity, audio, accuracy and depth with their past gaming experiences. However easy to pick up and play party games are excellent for introducing non gamers to video games, like Pacman and Tetris have been in the past.
Wii Play outperforming Zelda, Metroid and Mario Galaxy! The Wii certainly expanded the Nintendo userbase! My guess is that the userbase will double compared to the GameCube!