From the book Language of the Night:

Critics have been hard on Tolkien for his "simplisticness," his division of the inhabitants of Middle Earth into the good people and the evil people. And indeed he does this, and his good people tend to be entirely good, though with endearing frailties, while his Orcs and other villains are altogether nasty. But all this is a judgment by daylight ethics, by conventional standards of virtue and vice. When you look at the story as a psychic journey, you see something quite different, and very strange. You see then a group of bright figures, each one with its black shadow. Against the Elves, the Orcs. Against Aragorn, the Black Rider. Against Gandalf, Saruman. And above all, against Frodo, Gollum. Against him--and with him.

It is truly complex, because both the figures are clearly doubled. Sam is, in part, Frodo's shadow, his "inferior" part. Gollum is two people, too, in a more direct, schizophrenic sense; he's always talking to himself, Slinker talking to Stinker, Sam calls it. Sam understands Gollum very well, though he won't admit it and won't accept Gollum as Frodo does, letting Gollum be their guide, trusting him. Frodo and Gollum are not only both hobbits; they are the same person--and Frodo knows it. Frodo and Sam are the bright side, Smeagol-Gollum the shadow side. In the end Sam and Smeagol, the lesser figures, drop away, and all that is left is Frodo and Gollum, at the end of the long quest. And it is Frodo the good who fails, who at the last moment claims the Ring of Power for himself; and it is Gollum the evil who achieves the quest, destroying the Ring, and himself with it. The Ring, the archetype of the Integrative Function, the creative-destructive, returns to the volcano, the eternal source of creation and destruction, the primal fire. When you look at it that way, can you call it a simple story? I suppose so. Oedipus Rex is a fairly simple story, too. But it is not simplistic. It is the kind of story that can be told only by one who has turned and faced his shadow and looked into the dark.