"The Hobbit" was a trilogy of films adopting the novel "The Hobbit" directed by Peter Jackson. The trilogy was composed of: The Hobbit: An Unexpected Journey (2012), The Hobbit: The Desolation of Smaug (2013) and The Hobbit: The Battle of the Five Armies (2014). The film starred many of the same actors as Jackson's Lord of the Rings trilogy, and also introduced Richard Armitage as Thorin Oakenshield and Benedict Cumberbatch as the dragon Smaug. The films were commercially very successful, but had mixed critical reviews, especially amongst fans of Tolkien's works.
Most of the discussions about "The Hobbit" aren't about whether Peter Jackson can make an exciting, beautiful and fast-moving film. It would be a grumpy viewer indeed who wouldn't be impressed by the landscapes and effects that Jackson works into the film. The discussion is mostly about how Jackson chose to adapt the film, and brings up interesting issues of authorial intent and who a story "belongs" to.
The first thing to notice about this film is that it was turned into three films, much like The Lord of The Rings films. However, unlike the Lord of The Rings, "The Hobbit" was a much shorter book, telling a much more linear tale. Jackson took the story of The Hobbit, and worked in some other material of Tolkien's, as well as some original ideas of his own, to produce a film that is less a retelling of the Hobbit than an extension of The Lord of the Rings. And again, whether this is a good idea depends on how you view authorial intent.
And this depends even more on which author we are talking about: Tolkien himself had a long history with "The Hobbit", and intended the book in different ways at different points. Tolkien had invented the mythology that became "The Silmarillion" twenty years before he wrote The Hobbit, and the grand and tragic history of the elves was originally unrelated to The Hobbit, despite some coincidences in naming. It was only after he wrote the Hobbit, and was working on The Lord of the Rings, that Tolkien retroactively edited The Hobbit to make it related to his larger mythology, and to make it a more "mature" work, hinting at more serious themes. However, Tolkien decided not to rewrite the work too much, intentionally keeping it as an episodic children's book. Tolkien has also said, in other contexts, that the appeal of many aspects of a story is that they are not fully explained, that a story needs uncharted background to give it depth. When Gandalf departs from the company in The Hobbit to fight The Necromancer, it was not originally intended that The Necromancer was Sauron, and it was not originally intended to be part of a larger plot: it was just because Gandalf had to leave at that point to make the story more interesting. The Hobbit was an intelligent children's story, but it was a children's story, full of the shifts in focal length that characterize childhood, where things out of our concern are characterized in some vague "over there".
So out of what Tolkien had at first intended to be a simple adventure story, and later was an adventure story with subtle allusions to something larger, Jackson has constructed a history, a story where things are explicitly explained and directly connected to a larger background. There is quite a bit of world building here, and we get to see characters only mentioned in passing in Tolkien's works, such as the Wizard Radagast and the Elf-King Thranduil, as well as new characters (Elf Warrior Maiden Tauriel). All of this rewriting turns a comic adventure story where the logic of the larger story world is suborned to an episodic tale into a story that depends on world building, character development, internal consistency and all those other things we should value in a story. Whether you believe this is a good thing depends on taste.
My own view of the movies over all is that they are engrossing and beautiful, but have totally suborned the original feeling of the story. The movies title is a misnomer: rather than being the experiences of the guile hero Bilbo Baggins, the movies are a military history where Bard, Thorin and Legolas all overshadow Bilbo. Some of the book's best scenes were where Bilbo (or Gandalf) managed to outwit the powers around them. Bilbo's taunting of the spiders, verbal duel with Smaug and passing a message to Bard via raven, as well as Gandalf's shaggy dog story to Beorn are all foregone to have more gorgeous and improbable fight scenes. While I won't say I dislike the results, I do think that how true these movies are to Tolkien's story (and to its ethical implications!) is something that should be looked at with a critical eye.