The fellow below me is, in all aspects, correct. If what you look for in a dance movie is to be highly distracted by a shabby plot. Me, I loved Step Up 2 for this very reason...
Most dance movies aim too high: they want killer dance scenes -with- an excellent plot. What do most wind up with? Trite, familiar plots they still try to execute even though we've seen them before (so we know well enough to follow along) while still delivering a sliver or two of dance sequences... but nowhere near the amount the usual viewer wants to see.
Now, Step Up 2 says a big "yeah right" to that entire idea.
There is next to NO plot. Yeah, it's there, barely. Enough to pretend that it's not one long music video. But, it really IS like one long music video--and that's wicked awesome. The dance scenes are long and intricate, the music is great, and it delivers on everything I want to see in a dance movie: less talking and more dancing.
So if you're into these sorts of movies for the chick flick value, it might be a skip or a rent. But if you're into it for, well, the dancing--I give it 5 stars.