Well in that case it's probably rated for the target audience. A 5-star review of high-heel shoes wouldn't mean much to me, but for a woman they may be perfect.
You have to come to terms that the definition of "game" is expanding into territories you have absolutely no interest in.
Why should the score be reduced because you have a weird playing posture? I'm sure most people play like me: sitting on the sofa, Wiimote pointed at screen, perfectly comfortable. And what do you mean the sensor doesn't work when you're low to the ground? Do you play sitting on the floor?
It would be cool if the sale price was the permanent price. £12.99 is a lot to ask for considering you're only a couple of clicks away from the numerous Wikis that are available for a game of any complexity.