I bought this series after reading it myself for my 18 year old sister. I am 20 myself and I loved them.
While the writing can be likened to Twilight in that it is fairly simple, easy to read and easy to get into, the story is far superior. I was and am an avid reader - however my sister is more of a late bloomer. She read the first book in short order and we are both looking forward to seeing the film come out next month.
This is a perfect YA book but also a great book for older readers too. Although it is set in a future dystopian world, it only really gets dark in the last book. Definitely a tear jerker but definitely educational in that it really makes you appreciate the freedom that we have now.
A wonderful book series.