The only fantasy author I've read yet that was writing not to make a nice plot, but for good thematic qualities (at least, as his primary goal) has been Tolkien!
And what theme would that be? Elves are good; Orcs are bad? In times of need, just look to virtuous superheroes with magic powers/weapons for your salvation? That tradition and the "old ways" are noble and that industry and progress are sinister? Wow. How weighty, insightful, and original!
I first read Tolkien's work back when I was in school. Being young, and male, I found the tales of adventure in far off lands delightful escapist entertainment. Reading the books was a fun, if light, way to spend a few days. Later, when the movies were released, I enjoyed them as an equally delightful illustration of the books. Also escapist entertainment. But I've never considered the books particularly deep. In fact, I think one of the books' great failings to be its lack of theme and depth.
At its core, the story comes down to a battle royale between the forces of good and the forces of evil. Both sides being defined in terms not much clearer than that. Most of the characters are static, one-dimensional, carbon copies of classic fantasy stalwarts. You'd be hard pressed to find a dynamic character among them. Tolkien tries to compensate for this by giving his characters what I have come to simply call "fake depth." This is usually achieved by giving a character simple flaws, weakness, or flimsy back-story. Comic book authors have used this technique for decades; Superman is weakened by kryptonite, Batman had a rough childhood, the Hulk can't control his rage. It might be designed to make us see the characters as more human, but it doesn't give us any real insight into who the characters are.
This lack of true depth can also be seen in the fact that over the course of the books, none of the characters really go through any sort of arc. The characters don't change. They may become wiser, or go from cheerful to a bit more morose, but they don't change on a fundamental level. They have no greater understanding of the workings of the world or their place in it.
In addition the characters' motivations are never revealed (other than doing good or evil for good or evil's sake). All of the characters seem obliged to perform the roles assigned to them without much insight or reflection on their situation. The heroes perform heroic deeds because they are the good-guys, and the villains do evil deeds because they are the bad-guys. Nothing more.
Ultimately, no insight into the greater nature of man, either on a personal level or on a collective level, can really be drawn from Tolkien's work. Acceptable works of literature are defined by their plot. Great works of literature are defined by their characters. And great characters are defined by their actions, not by hackneyed character flaws. To compare Tolkien to Melville or Twain is to lessen the impact of their work. It does little to elevate Tolkien's work. Ahab and Huck Finn were dynamic characters whose actions were defined by, and were the result of their personalities. Character's who cannot be broken down simply into a list of their virtues and flaws. The same cannot be said for characters like Frodo and Bilbo whose personalities existed simply to provide believability for the actions the plot required them to take.
Perhaps the quality of Tolkien's work doesn't require a dissertation, but I grow so tired of Tolkien being elevated to the status of literary titan when he's little more than a capable author of fantasy pulp. To compare Tolkien to Melville, Twain, or Hawthorne is to compare Spielberg to De Sica, or John Williams to Mozart. I found the works of Tolkien entertaining. But great literature, it is not.
-Phil.