I just finished re-reading this book after I read it when I was maybe 11 or 12? 
It's good book with a unique idea and setting that is really timeless. 
This book is very interesting with is dialogue about emotion, pain and choice in feeling. It talks about how pain, sadness and anger - all those 'bad' emotions - and happiness, love and joy, - all the 'good' emotions - are intertwined and cannot be separated. There is no way to feel only the 'good' or 'bad' emotions. If you have emotions, you have to feel both. 
The people in this community, they don't feel anything, their emotions are dulled, their relationships unfulfilling, but they have no way of knowing that, because they have nothing to compare it to. 
For everyone, emotion is something that is so core to us, it is our drive and gives us reasoning and motivation to do things. This community don't have that, and it's very interesting to compare them and the way they live to modern society. 
Also brought up is choice. People in this society don't have serious choices. They can't choose their jobs, or their spouses or even their children. Everything is given to them, and they take what they get. Jonas chooses to have choice, but this comes at the cost of the stability, peacefulness and ease of his previous life. This fits alongside modern discussions of free will and responsibility of actions. 
Some things I think this book could improve on is length. This book is rather short, and if it was longer, characters could be more fleshed out and developed. Characters like Rosemary, who we barely learn about, could be expanded on, and we could see the actual impact of her actions. 
Jonas needs more time to decide he wants to defy the Elders and change the life the people of the community live. When I read about him deciding to do that, it didn't make sense to me, as he didn't really seem to have much reason or motivation to do it. 
But that is my only real issue with this book. Other than that, this book is a timeless classic that I would definitely recommend.