One of the main themes of Lord of the Rings is development of character. The four hobbits came from a type of people that did not partake much in the world's event and did not effect its course either. When they began their journey it is not apparent of their importance to the quest. This was strengthened by their physical size and the fact that they couldn't ride horses. However, as the story nears the end, their role in the journey is now seen as one of the most important, probably the most important. However, Peter Jackson leaves out one of the most significant parts of LoTR, the recapturing of Hobbiton from Saruman. In the novel, the four hobbits enter their hometown riding (if I remember correctly) horses. They take command of the rebellion. They essentially become generals and would lead the other hobbits defeat of Saruman, much like Aragorn, Legolas, Gimli, and Gandalf.
I always felt that the film adaptation was incomplete. Peter Jackson did add that scene atop Minas Tirith where all the Men and Elves knelt for the Hobbits(a beautiful scene by the way), which did help for the completion of the hobbits' transformation from a fun loving and careless people to an essential force in the fight against Mordor.