I kept going back and forth over 4 or 5 stars, so I'm splitting it down the middle. I loved DIVERGENT. I had high expectations for INSURGENT, which is why I'm floundering on the rating. It is a phenomenal book, great adventure and intriguing ending. For better or worse, I hold Roth to a higher standard than other authors because she's set the bar that high for herself.
My main gripes was that it doesn't recap enough of what happened in DIVERGENT for a sequel. It had been some time since I read the first book and found myself a little lost with the second. The heroine, Tris, also seems to encounter situations that don't necessarily advance the plot, but put her in bad circumstances for the sake of action.
These two points, however, is me nit-picking. Overall, I found the book highly engaging. I read it on my commute to and from, and never wanted to put it down. Very excited for book 3.