I've bought a number of copies for my family through Amazon. I have to say that there very few used copies available throughout its existence.
Just Dance's success shouldn't come as a surprise. Very low barrier of entry (excellent social lubricant during a party), instructions on front and back of box or personal experience, minimal penalties that don't bog down the pacing, contemporary if limited soundtrack, aggressive pricing, excellent ad campaign by Ubisoft (HA-HA!), viral on youtube through countless home videos, and much more. It takes a lot of talent to make a game very approachable, physically demanding, and genuinely entertaining. Perhaps Ubisoft took a good look at how the early Wii/Wii Sports phenomenon, why it occurred, and replicated it with considerable success. Of course, give Ubisoft a few installments before they run this to the ground.
It really goes to show how detached reviewers are from consumers. This isn't a movie reviewer saying a movie is intellectually bankrupt and viewers finding it an enjoyable dumb film. This is a reviewer telling you the game is not fun and countless consumers finding it to be the complete opposite. The Worthplaying, in particular, is baffling with its attention the game's graphics and presentation. It reminds me of the early Pokemon Red/Blue reviews.
It seems arcade game design common and very popular in the 70s and 80s have left people today completely flabbergasted when a game like this becomes a hit. It's like the game's very existence has physically harmed some posters in this topic. I haven't had this much fun since people started to call New Super Mario Bros. Wii a non-game! God, the Wii is easily the most entertaining console ever created. Not because of motion controls, blue ocean theory, or Mario Kart Wii, but because of how utterly insane it's making everyone!!