I had a little go on this game recently and I've got to say I had a lot of fun with it and I'm not suprised it is enjoying good sales figures.
Whether or not you think it's disrespectful to have a dead celebrity endorsing a product is kind of irrelevent in cases like this. This game felt more like a tribute than a cash in.
It's dance mechanics are well implemented and a lot of effort went into it's design, the gameplay isn't perfect but then again it's better than most wii games i've played.
Dancing games are not new to the world and given the latest bout of motion-controlled interfaces, games like these are going to become more and more predominant in the casual game market. The idea that Michael's music and legacy should be laid to rest is nonsense! Should they have stopped putting on performances of Shakespeare's plays because he died? Of course not, and this should be no exception. MJ was a supremely gifted performer and this game I think helps to paint a more positive light on his career with a sole focus on the dancing and singing for which he became world famous for. I think a lot of this negativity comes from those young'ens who weren't around when Jackson was still in his prime, those who were knew how special he was then and after his death didn't need a Media-driven 180 to discover it.
Though i'm not rushing out to buy it for myself (dancing is not something i'm particularly fond of), I can see a lot of potential for similar games focusing on more than just dead popstars. There is a whole host of West End Musicals, Film musicals and Bollywood films which would make a solid impact on the casual game market... Just because John Travolta is another scientology nut jub with a failing career doesn't mean you can't find hundreds of thousands of people out there willing to pay to pull of 'those' dance moves from Saturday Night Fever.