Yes, it is young adult fiction and somewhat repetitive in nature; but that is not all there is to The Unwritten Rule. There are ethics, guilt and conscience involved. The personality of the protagonist did help, too. It could have been more exciting, but considering the simple way it is written; it really isn't need be.
I really liked the way Elizabeth Scott has portrayed the antagonist. You feel this empathy for her; but, also anger at her for being the way she is to no fault of hers. She could have been more understanding, though. But then I am aware that there are bitter end to friendships.
This was my first Elizabeth Scott book and I look forward to reading more from her. The Unwritten Rule has deeper meaning to it than just the so-called 'cheating on your BFF' theme. It is about making hard choices and knowing that you wouldn't take them back if they had the slightest chance to alter the course of your life. A must-read!