The Hobbit is certainly an example of the hero's journey. The lead character is stuck in a rut, forced out of his norm, goes on a journey, confronts challenges, succeeds, then returns home changed. This is the formula of a hero's journey.
However, there is a clear deficit in The Hobbit in terms of creating a compelling story. Bilbo really doesn't have anything he cares about other than his way of life. He doesn't have a family or something that means more to him than life itself that explains his reasoning for taking the journey. He does have an attachment to his lifestyle, but it doesn't seem like something he is wholly invested in because he later makes the decision to leave his home and way of life to go on his journey.
This is not necessarily a bad thing in a hero's journey. The other option would be to have the lead be coerced or forced in some other way to take the journey, but Bilbo chooses to go on the journey. This is my primary criticism of the story, there's no visceral reason why Bilbo chooses to go on the journey and no real logical reason either.
In the same vain, he learns about a journey he can choose to go on by total chance. Gandalf seems to just be walking past and Bilbo just happens to be out smoking his pipe and say "good morning" to this man that he does not recognize. This meeting is not really set up, save for some vague references Bilbo makes to his childhood.
Beyond the deficient (in my opinion) setup, the rest of the novel follows the conventions of a hero's journey, which is a very compelling and tested model of a plot. The interest is created through the new world created by Tolkien that the reader can't help but be invested in. The detail of the world and the eccentricity of it is very compelling and sure to hold any reader.