My teenage kids were raving about this so I gave it a go. I loved it, and rushed to read the second book in the series.
I think the new world created in the book is very believable and engaging. It is set in a future, post apocalyptic world where society is trying to recover form some devastating events (which are never explained). There are five Factions, everyone on their 16th birthday has to choose to be part of one faction. It can be the one they are born into or they can go to another, and be absorbed into a completely different lifestyle and role in society.
The Factions are:
Erudite (The Intelligent): they are dedicated to knowledge, education, technology, research.
Amity (The Peaceful): they are the ones who nurture relationships, the pursuit of love, life and freedom. Their role is to grow the food for all the factions,
Abnegation: (The Selfless): they are all about being selfless in every act they do, thinking of others only, never themselves. Their role in society is to govern.
Dauntless (The Brave): they are the defenders, the aggressors, warriors and are fearless.
Candor (The Honest): the truth matters above all else. They provide society with law and it's keeping.
The main protagonist is Tris, who chooses to become Dauntless. She's a strong, credible heroine and the story is worth reading. Movie coming out soon.
You can also impress those teenagers around you by asking what faction they would belong to...Interesting conversations!