I'm quite shocked at the reception of this title. I wanted to create this thread early on, before its sales trend becomes too obvious. That way we can go back to this thread months from now and laugh at the crazy predictions!
So, where do you think this title will end up? December NPD had Just Dance at the ballpark of around double VGC's estimation, so keep that in mind.
I'll go for the bold prediction of over 3.5 4 million.
I know this may sound a little crazy, but I see the title having great legs, as it has practically no competition in its genre. Its sales skyrocketed in the UK, in its 8th week after release, and this is out of the holiday season. The customer reviews this game is getting is unlike previous third party hits, see Amazon for example (US / UK, almost all 4's and 5's). It's about as accessible as it gets, and the game's premise, dancing, has extremely broad appeal.
I believe it started slow because it's an unknown IP, so even with the advertisements people are weary of spending their money on it. Word of mouth will get around, and it'll soon become clear that it doesn't require the "Nintendo" name on a box to make a massive leggy hit.
The best part about all this is its metacritic is currently sitting at 45.
Now, what it does have going against it is it's a 3rd party title. That means that because it's a hit, we can almost expect a "Just Dance 2" by next holiday, which will kill its sales (whereas Nintendo wouldn't opt for such a thing). Hopefully that wouldn't sever its legs completely, and limps on to my prediction...
