Regardless of how long these films are or how many they are, the first mistake in the film is that it begins with a lengthy prologue. Fine for the the LotR films, and that prologue was carefully written to only lightly touch on historical events while remianing true to one factor: the POV in that prologue is the Ring's. This was a great movie for a number of reasons.
I believe that Hobbit needed no such prologue. Begin with "A hole in the ground there lived a hobbit" and have Bilbo learn much of that back story from Thorin and Gandalf.