My favored definition of wisdom has always been 'a recognition of one's limits', and as such, wisdom is vital for writers. When an author knows their capabilities and their flaws, they are in prime position to write a story which takes advantage of their strengths and mitigates their weaknesses.
Yet what is preferable for an artist: to stay within the bounds of their skill, or to work to always to exceed them? The first sort will be able to create precise and deliberate works of mastery, while the latter can produce wild and intense works of vision. All authors experiment and take risks while writing; should such experiments be left in, even when are not entirely successful?
There are works, like Moby Dick, which are masterpieces precisely because they are full of numerous, unusual experiments, not all of which were effective. Many critics are hesitant to praise works which are grand, yet incomplete, stitching together many wild ideas and disparate techniques to create a vision which is powerful and inspirational, despite being conflicted.
In fantastical genres, it is perhaps an even more central question, since they are so dependent on the strength of idiomatic vision. Perhaps the clearest illustration of the importance of that creative force is the vast influence of pulp authors. Their style was defined by unbridled exploration and a thirst for new ideas. They went headlong into the fray without pretension, for authors who erred on the side of caution tended to be left behind. What they lacked in style, character, and plot they tried to overcome with an abundance of ideas.
In horror, the line between restraint and unfettered creativity is usually defined by what the author chooses to describe, and what is left to the reader's imagination. As many a skilled writer has demonstrated, the reader is often better at scaring themselves if the setup is strong enough. The strongest example may be when the author begins to describe some terror, then breaks off with 'but it was too horrific for words to describe, too awful to comprehend, too shocking for the mere mortal mind to revisit'.
Though many authors--particularly of the Victorian--use this technique, I tend to associate it with Lovecraft. It has been a running joke in my writing circle that Lovecraft's monsters are not actually that terrifying, it's just that his protagonists are so nervous and sensitive as to be totally unnerved even by the least imp.
Machen uses this technique throughout the story, leaving much of the action implied so that we must piece together the reality from the occasional detail. His constant drawing back from actual descriptions helps to remind the reader that, for the purposes of a story, what the Thing looks like, or what it is capable of are not fundamental to the story itself. The story is about people, about their reactions and the progression of events, and if the structure is strong, there is no need to explicate the monster.
Machen's writing is competent and precise--he does not give in to the purple prose and long internal monologues which typify Lovecraft, nor does he trudge along, workmanlike, in the manner of Stoker. The gradual unfolding of the story and its mysteries is artful, and the uneasy tone consistent.
Yet there are problematic aspects. The characters are not vivid or well-differentiated, which makes them difficult to connect with, and the story harder to follow. We are often casting about between different individuals and their experiences, and since they all speak in a similar voice and have similar backgrounds, it can be a task to keep them apart.
And while the gradual unfolding of the action is enjoyable, the structure is somewhat imprecise, going back and forth and sometimes repeating itself. Though Stoker was rough and guileless and Lovecraft often overwrought, at least they both focused on the central motivations and desires of their characters throughout.
Despite these flaws, it isn't difficult to see why horror authors from Lovecraft to King have cited this story as an influence, and have worked to recreate its haunting, slow-burning build.