To objectively judge writing skill, one must use the accepted standards for the type of writing. Types would include fiction, non-fiction, journalism, essay (with various sub-types), etc. Letís focus on fiction prose.
Fiction plots have accepted standards, differing a bit between short story, novella and novel. The basics include conflict(s), characters, rising and falling action, etc. Any 1st year Lit student should have been exposed to these ideas. Also under consideration could be development of a theme, use of viewpoint, dialogue, voice, and a few other factors.
Fiction can also be classified into one of four possible categories, depending on plot development. A Milieu story is written to explore a setting/world, whether created by the author, which usually is the case in fantasy or sci-fi fiction, or not. One such story is Barbara Hamblyís Dragonsbane. The plot carries the reader throughout Hamblyís created world. An argument could be made that a milieu story could also include the contours of the psyche, such as that of a deranged or psychotic person.
A Character story is written to show change in one or several characters, usually due to some event or circumstance in life. Although I dislike using such an insipid example, Jane Austenís Emma is such a story. Emmaís heart changes due to a series of events in her life, until she realizes that she does indeed love her much-older gentleman neighbor.
An Event story focuses on just that, an event or series of events. The Indiana Jones movies are great examples of this type of story. We thrill at the intrigue, explosions and romance, but the characters are static. Indy is the same guy before and after the story.
An Idea story generally focuses on a question to be answered. A good example here is any mystery, such as Agatha Christieís ĎWhodunnití type of stories. The reader is led, clue by clue, to the answer to the question.
Because of its extensively developed backstory and deep lore, I am a devoted fan of Lord of the Rings. What really makes the LotR so successful is Tolkienís genius. He was able to successfully incorporate all four types of stories into one. The Hobbit and Lord of the Rings are, without doubt, milieu stories. The reader is carried across vast distances, visiting numerous fantastic locations throughout the stories. Also present is the character story. Aragorn, Bilbo and Frodo are the primary candidates here. They are changed to such an extent that one moves from self-exile to king, and other two have to leave their native land because of the long-term effects of the ring.
Events of numerous natures are present in LotR, the primary being the destruction of the One Ring. The series of events and encounters leading to that ultimate deed are why Jackson was able to make a successful movie. We Westerners need events in our movies, or we often feel cheated out of our ticket price.
Of the Ideas present in LotR, some are obvious while others are more subtle. Clearly, we have Good versus Evil. More subtle is the idea of social change due to the influence of evil. When Frodo left the Shire, life there was romantic, pastoral and relatively carefree. By the time he returned, Saruman and Wormtongue had defiled the Shire by cutting down massive amounts of trees and turning the place into an industrial outpost. Frodo and company are forced to deal with the situation, returning the Shire, as best they can, back into the idyllic setting is once was.
We can judge writing using the objective standards set by culture. As someone stated before, culture changes. Reading Dickens can be a nightmare of character introspection and deep detail, although his work is worth the extra effort. That style of writing is not tolerated in modern Western publishing or reading.
Iím not familiar enough with Dune, as was mentioned in comparison with Tolkien, to evaluate it properly regarding the four story types mentioned.