I really enjoyed the idea of this story. I also thought that it was executed fairly well. What I didn't appreciate was the very end. It finished up kind of abruptly. The second book in this series needs to come out soon, because that end has zero closure whatsoever!
Lena and Alex are a great couple. Lena's friend Hannah is a good character, and I loved her dissent and challenge of the rules. She plays an important part in Lena's transformation throughout the novel. Alex is something special on his own. He's brave, but he's a liar. I wasn't sure if I could trust him right away. But the narrator's voice for him made me fall in love with him a little bit too.
Speaking of the narrator, I didn't really like her voices for Lena's Aunt Carol or her sister. I think Rachel is her name. I did like Lena, Hannah, and Alex quite a bit though.
I would recommend this book based on the idea alone. What would you do if they found a "cure" for love?