Even though I don't generally like them, I can handle an unreliable narrator. What I don't like is a manipulative author. Liar is an enjoyable read, but you end up irritated with it in the end. Therefore, I don't know whether to recommend it or not.
Content--a teen who is not especially socially successful secretly dates a popular boy who ends up dead. She's got a secret that points to her involvement in the boy's death, but it's one unbelievable secret. I choose to believe her, but probably you're not supposed to. I don't know and don't care all that much. I'm not one for arguing literary ambiguities.