The Hobbit General Changes
Pro: The changes add depth to the story and meet the expectations of fans of the Lord of the Rings films. Tolkien himself revised The Hobbit in a later edition to better tie it into his later work, The Lord of the Rings.
Con: These films are too long, mature and violent for what is meant to be a children's story adaptation. The first film, An Unexpected Journey, has been widely criticized for being bloated, overlong, unevenly paced and too violent for young children.
The Bagginses of Bookend
Book: The book opens with a couple of pages of narration describing the life of hobbits in general and that of Mr. Bilbo Baggins in particular. The first lines of dialog involve Gandalf approaching Bilbo standing outside the door of Bag End and announcing that he is looking for someone to join in an adventure. Frodo, whose birth does not come until 27 years later, does not appear in the story.
Pro: Having the familiar faces of Holm and Wood appear in scenes that “bookend” the three Hobbit films serves to draw interest of fans of the Lord of the Rings film trilogy. It also reminds the audience that Bilbo’s adventures served as the catalyst for the events chronicled in The Lord of the Rings.
Con: These new scenes of Bilbo and Frodo would undoubtedly require the invention of dialog not found in the original book. Besides, the inclusion of Gandalf (not to mention Elrond and others) serves the same purpose.
Book: Although Bilbo was 51 years old at the beginning of The Hobbit and 111 when he departed Bag End in The Lord of the Rings, the book states that the passage of time had little effect on Bilbo. “At ninety he was much the same as at fifty. A ninety-nine they began to call him well-preserved, but unchanged would have been nearer the mark.”
Pro: It was not feasible to have Ian Holm play Bilbo again in the action-packed Hobbit films. As it was, the elderly actor filmed his bookend scenes entirely on a soundstage at England’s Pinewood Studios.
Con: The Ring’s slowing effect on Bilbo’s aging process is an important plot point. Even in the Lord of the Rings films, Gandalf observes that Bilbo “hasn’t aged a day”. Showing old Bilbo and his younger version in the same film calls to attention that they are played by different actors with a wide age difference between them.
Book: Bilbo wears only the Hobbit clothes he wore the morning after the dwarves arrived at Bag-End.
Pro: The hobbit clothes without a cloak make it easier to visually distinguish Bilbo from the dwares.
Con: The beardless Bilbo is already easy to distinguish, and the elimination of this detail also diminishes the early friendship forming between Bilbo and Dwalin.
Radagast The Birdcage Liner
Book: Radagast is indeed one of the five Wizards, or Istari, whom the Valar sent to Middle-Earth in the guise of old men to aid the Free Peoples against the return of Sauron. However, Radagast appears in The Hobbit only by name when Gandalf mentions “his good cousin Radagast who lives near the Southern Borders of Mirkwood” to Beorn. Gandalf again refers to Radagast in The Lord of the Rings, when, during the Council of Elrond, the gray wizard explains that Radagast the Brown delivered Saruman’s message summoning Gandalf to Orthanc.
Pro: Radagast lived close enough to Dol Guldur that it reasonable that he would have played a part in the White Council's investigation into the Necromancer during the timeframe of The Hobbit. The bird-droppings is a humorous representation of Radagast's affinity for birds and beasts and disinterest in the ways of Men and Elves.
Con: Tolkien never described Radagast as having birds living in his hat, and showing the Brown Wizard as being covered in bird droppings is counter to the noble nature of the Istari. Nor did Tolkien describe Radagast as having any involvement with the White Council against the Necromancer. Giving Radagast a role in the events of The Hobbit will require the screen writers to invent other details and dialog for Radagast that Tolkien did not intend.