Insurgent

The Book

Having foiled the attempt by Jeanine Matthews and the Erudite to mind control the Dauntless to do their bidding, Tris, Tobias and a group of rebels are pursued as they move from faction to faction. The visits to Amity, Candor and the factionless give us a bigger picture and help flesh out the differences within the different groups. It also brings together characters from each faction, where familial and friendly loyalty sometimes overcomes the faction traits.
Jeanine continues to pose a threat, expanding her control to include Candor and experimenting on Tris in order to overcome the Divergent strain that is resistant to the mind control serum. 
The last 100 pages are non-stop action, whereby the factionless and Dauntless team up to storm the Erudite's fortress, which is protected by controlled Candor.
The second book in the trilogy is much more satisfying to read and provides at least some explanation for the strange divisions in the society, with a grand reveal at the end:



outside the fence, society was breaking down and the factions were set up as an experiment in order to develop the Divergent.  
It's still a totally preposterous set up, as whoever thought that by dividing society they would find a solution to peace. Oh fore-fathers! 

Official movie website


The Film

It begins by playing with audience perceptions over what is real and what is imaginary, as Tris wakes from a dream that starts pleasantly enough and then she is confronted by her guilt at killing Will and the death of her parents. This is a sign of things to come.

The plot diverges from the novel when Tris gives herself up selflessly to Jeanine to prevent further controlled suicides. This means that the film writers rejected a large scale battle in which all the factions take part and instead decided to go all out on special effects. The film wallows in Matrix-like simulations where solid objects break down into pixels and Tris rescues her dead mother from a floating, burning building. If she can later realise a fake rescue via something Tobias says, surely she would realise that this was not a real situation!
As visual eye-candy, it's ok but because it's unreal, it loses footing. What works much better is the realisation of the apocalyptic city, as Tris, Tobias and Caleb make their way to Candour. This is all for Jeanine to open a glowing box that holds the proof she thinks justifies her stand against the divergent.
It was great to see Shailene Woodley and Ansel Elgort, the two actors from Fault in our Stars, sharing screen time together again as Tris and Caleb, even if their relationship here is far darker.