Summary: I have both Dance Central (all of those) and this game, and I must say this game makes you sweat much more. If you're looking to loose weight, I recommend this game. The lasting appeal may not be as long as DC, and they're certainly isn't as many songs, but the songs and dances they do have are pretty good. Some are little awkward and feels a little in-human to me, but songs are good.
Summary: I've both Just Dance 3 and 4. JD3 is simple and fun. JD4 is a bit complicated to navigate at the beginning but it definitely has more robust and moves are better coordinated given it is later version than 3. If you have to pick one, I'd get JD4.