Tris and Four are back, only five days after the end of the previous movie. They're hiding out in Amity (one of the factions), but get in trouble when Peter (Miles Teller) deliberately provokes Tris into a fight - Amity believes deeply in non-violence. They end up looking for the Factionless and the members of Dauntless who left Dauntless after the Abnegation massacre (which is weird, because the whole point of the previous movie was that Tris and Four just barely prevented that massacre ...).
The writing is better in places: Veronica Roth (the author of the original book) was trying to write characters in the first movie who were morally ambiguous, but it wasn't very effective. This time it's working better. But the action sequences - even if some of them are "in a sim," are often way stupid and over-the-top (but you have to wonder if that's the fault of the author, the screenwriters, or the director). And Woodley's acting is starting to get on my nerves. She's doing a fine job of the sobby teen girl with too much weight on her shoulders, but she's not bringing much depth to it. And you need some depth when you're running for three-plus movies. So it's a wash - still mediocre SF.