Just to start out to recognize the work that has gone into this, and the research. Though there are significant concerns, I hope they will be addressed and worked on and more eyes brought in to work on this for the next review. Good luck !
WP:PLAGIARISM: I saw this post [1] from the talk page archives. So I went back and compared with http://www.sparknotes.com/lit/fountainhead/summary.html -- unfortunately, there are definitely similarities. Suggest scrapping the entire "Plot" section and re-writing it from scratch, so as to avoid these plagiarism concerns.
WP:COPYVIO: Much more of a minor issue. Certainly much easier to fix. I just think the blockquote is unneeded at section, "Ellsworth Toohey", and also some quotes throughout the article can be reduced, removed, or paraphrased away.
Intro section: First paragraph is two-sentences-long. Seems quite short. Last paragraph is two-sentences-long. Judging by the size of the overall article, the entire introduction section could be greatly expanded into four healthy full paragraphs.
Concerns about overly long sentences throughout the article. Example: "The book follows his battle to practice modern architecture, which he believes to be superior, despite an establishment centered on tradition-worship." and "How others in the novel relate to Roark demonstrates Rand's various archetypes of human character, all of which are variants between Roark, the author's ideal man of independence and integrity, and what she described as the "second-handers"." If you have to use more than one comma, or even more than two commas, then that sentence probably needs to be cut in half, or thirds.
Suggest getting a couple of previously uninvolved people not familiar with the topic but good at English to copy edit.
2. Verifiable?: Very good citation style. Very good References and Works cited sections.
3. Broad in coverage?:
Intro section seems quite skimpy, as noted, above.
For such a known work, the "Themes" section and subsections can probably be expanded with a great deal more scholarly academic sources.
"Impact on Rand's career" can probably also be expanded as I'm sure there is more to this.
"Adaptations" this section could also be expanded more.
"Illustrated version" what was the reception for this?
"Theatrical version" what was the reception for this?
"Film version" what was the reception for this? We only have Rand's reaction, herself. Therefore this violates WP:NPOV.
4. Neutral point of view?:
Concerns about NPOV in the article.
Not seeing much of reception, positive or negative, of any substance, in the intro.
Use of word, "However...", at five times in article, seems to violate NPOV, as if hedging, eg: "The film was directed by King Vidor. The Fountainhead grossed $2.1 million, $400,000 less than its production budget.[122] However, sales of the novel increased as a result of interest spurred by the film." This seems to violate WP:NPOV. One is not related to the other. The film production crew and staff, film director, etc, do not get those revenues back from the book sales. These are two different things. The "However" there, suggests wider POV problems.
5. Stable?: Article edit history stable going back to October 2016. No ongoing talk page conflicts.
6. Images?: Book cover image page could be improved using ((Non-free book cover)).
Overall, concerns about violations of WP:PLAGIARISM, WP:COPYVIO, and WP:NPOV, as detailed, above. There is indeed great work going on here, but several items to address before the next attempt at review. Good luck !