Update from Oct 25, 2015: I've rated this down to 2 rather than 3 stars, because the hype surrounding this book keeps jangling my nerves, and the more time passes since I've read "Divergent", the less do I like the aspects I remember from it. 
 Review (written on Jul 28, 2015): 
 2,5 stars, rounded up to 3 stars. 
 First off, I didn't nearly hate this as much as I simultaneously enjoyed it, yet neither do I understand how this became such a well-known bestseller. Veronica Roth introduces a self-confident, complex and likeable heroine, accompanied by a sexy, charming, strong leading male with a dark background (well, what else are today's protagonists supposed to be?) - two characters I grew to like a lot. The story included very interesting scenes [for example the fear simulations, the initiation phases, the ride down the zip line with Tris, Uriah and the other initiants] - and an interesting build-up ... but the author did not succeed in making me care about what had happened in this dystopian world. 
 In the beginning, it seems to be a given how Chicago is divided into five different sections. Veronica Roth did not explain it at least once, which is why I probably have to read ,,Insurgent" or even ,,Allegiant" in order to learn information about the background, but with this being the only reason for me to continue to read the series, I probably won't do so. I already have enough books on my ,,to-read"-shelf, and I think the ending is satisfying enough to stop reading after book one. 
 It was no bad read, don't get me wrong. Tris and Four are very slightly interesting characters, and there was NO love triangle (yippie) - even though I initially feared to have to endure this, after one of the other characters showed his interest in Tris. The writing was floppy at some places, though. A LOT of sentences were simplified by boring and-constructions (perhaps in order to avoid this book from developing some complexity); several dialogues very anything but realistic. Yet Veronica Roth produced some well-written fight scenes, the development of Tris' character was felicitously performed, and Christina, Caleb or even Tris' mother were well-developed supporting characters. 
 I usually try not to do this, but I will probably look for some more detailed summaries of ,,Insurgent" and ,,Allegiant", allowing this series to rest in my ,,series-I-probably-will-not-finish"-shelf. It certainly wasn't awful, but neither was it awesome.