Dr. Craig S. Keener is professor of New Testament at Asbury Theological Seminary. Here is roughly fifteen minutes of video which has him distinguishing the literary form of ancient from that of modern biography: Keener post at the Centre for Public Christianity.
HT: Brian LePort at Near Emmaus
See also this post on Richard Bauckham, a British scholar who has also researched ancient biography as a literary genre.
The gospels are biographies but they are not shaped like the biographies we are used to reading. These two scholars explain how biographies took different shape in ancient times. They will help you clear away false expectations and see the life of Christ in the gospels more clearly.