I just finished reading Tim Keller's The Prodigal God: Recovering the Heart of the Christian Faith. It's incredible. And it's short. You could probably read it in two hours, maybe less. It is a succinct, inspiring challenge to commonly held understandings about the Christian faith. Keller expounds on the parable of the Lost Son from Luke 15 and rightly points out that the point of the parable was as much about the elder son as the younger. One line early on literally made me put the book down, shake my head, and say out loud "Wow." I don't want to give it away. You'll just have to read it.
In the second half of the book, he paints a picture of the kind of biblical Christianity that is truly inspiring and made me want to say: That's what I'm TALKING about, Tim! So check it out.