I have an unashamed love for Wrong Side Of The Tracks dance movies while being perfectly capable of recognising that their usual range of quality falls somewhere between "not good" and "excrutiating". Most feature at least one lead who cannot. act. at. all. Some feature two. In the real humdingers, not only can neither of the leads act but neither can any of the supporting cast, either.
However, they can all dance, which is really all that matters in these films.
Step Up is better than average, which puts it somewhere around "not bad" in terms of actual quality. It's no Save the Last Dance, but StLD came out of nowhere and confused the entire Dance Movie issue by actually being a good movie. (Its sequel, however...)
Step Up was, I gather, Channing Tatum's breakout film, and as he can in fact act as well as dance, he wasn't embarrassing. There were even moments when he emoted. The female lead was...not quite as good as Tatum, but almost entirely not cringe-inducing.
The supporting cast was actually pretty good, with the exception of the Best Friend's Younger Brother, who was deliberately over-acted, but not, I think, to the effect they hoped. The Best Friend (played by Damaine Radcliff) was actually really good, and also about 19 feet tall. I don't have the impression Tatum is a small guy, but Radcliff towered over him. :)
Anyway, not bad, as these things go. Better than 3 & 4, which are the only two of the 5 I've seen (and Sarah Rees Brennan has still not, I think, forgiven me for making her go see 4 with me, although I *told* her it wasn't going to be good... :)), so now I'm kinda looking forward to watching 2 and 5. :)