Insurgent picks up directly where Divergent left off. It's almost like they're not two separate books at all, just different parts of the same book, because usually different books pick up a while after the first one left off, and there is something of a recap to what has happened. This didn't happen with Insurgent.
I think I liked Divergent more than Insurgent, but I still really loved Insurgent.
It really seemed that the real characters came out from under the hard shell they have on the outside. Every single one of them, in Insurgent we learn about how the characters really are.
Tris turned out to be a selfless person through and through, but she was a bit of a wreck after shooting Will (it happened in Divergent), maybe even overly so. But she got through it in the end, which is good.
In Insurgent, Tobias and Tris are having a couple of problems. Tris is just trying to do what she thinks is best for everyone (even if that means sacrificing herself) and Tobias, instead of trying to reason with her, spends a lot of their time together yelling at her, believing that she doesn't value her life. I kind of get where he's coming from, with that, but I also understand Tris' side of the story. Kind of strange. I like how they have these fights. Well, obviously I didn't LIKE it, but I think it was good because it let us know that they weren't some fairy-tale couple, where everything is always okay.
Grrr... I don't like cliff-hangers much. Veronica Roth is going to write another book right? I'd hate to be left hanging for the rest of my life, even though the cliff-hanger was really good, making it all mysterious and everything.