There is a plot, of sorts: Step Up 2's Moose (Adam Sevani) goes to NYU after promising his parents he'll stop dancing. But when he literally stumbles into a dance-off, he meets a dance crew called The Pirates, and promises to take part in the World Jam.
The Pirates are a rag-tag group led by Ashton Kutcher lookalike Luke (Rick Malambri). Add in a pretty, mysterious love interest, cliches galore, a rich bad guy, a seemingly insurmountable setback and voil? that's the plot.
But that's not what you're paying for. What makes this film so enjoyable is the almost constant deluge of dance - from the odd step that none of the characters seem capable of holding in, to the reality-defying, larger-than-life routines (the burst hydrant and Astaire scenes are particularly glorious).
And when you actually feel like water is about to splash you in the face, or a hand is going to knock off your dorky glasses, you know the 3D effects are worth it. Take note, Tim Burton.