Take a look at the reviews at Amazon UK. I've never seen such complete gushing over a product on Amazon before. Great products average 4.5 stars; Wii Fit has five.
I do think it's reasonable to ask whether this almost silly level of love at first sight will continue as people continue to use the product after the first few days. However, we might just be seeing the beginnings of something that transcends "hit" on the way to "phenomenon."