As other reviewers have said, the lead character in this film is now played by Izabella Miko, not Julia Stiles. Immediately this ups the credibility of the ballet dancing - and gives us a less able actress in the lead role. You win some, you lose some.
Miko actually isn't that bad, she's just not a patch on Stiles.
Given that the action has moved to New York and "my boyfriend and I decided to see other people", this means we lose any real continuity with the first movie.
Columbus Short however as the love interest is easy on the eye and pretty good in the role, though the lead couple don't really have the chemistry to make it completely believable.
Jacqueline Bisset is formidable as the scary ballet mistress who makes Sara's life a misery, and there are some other good supporting performances.
To watch, it feels like a long-ish movie, even though it's just 80 minutes long. I think probably because of a worn out plot and no huge surprises or plot twists (there's just the one, which I found pretty unbelievable, so it didn't really hit home).
All in all, it's an OK movie: for a chick flick or a teen night in, you could do better but you could also do SO much worse. However as a sequel to a strong movie like Save The Last Dance, it falls rather flat, and certainly doesn't conclude nearly as strongly as the first did. It would have worked better as a stand alone movie, although of course you can understand the desire to build on the success of the hit.
Overall, it's fine: some good music on the soundtrack, some decent performances, some good dancing and a couple of really clever shots cinematically. It's reasonably rewarding to watch. Just don't expect anything of the calibre, thematically or in terms of the quality of performances etc, that you saw in the first movie.