The phrase "a long introduction" is correct and usable in written English.
You can use it when referring to an introduction that is extensive in length, often in the context of essays, speeches, or presentations.
Example: "The author provided a long introduction that set the stage for the complex themes explored in the novel."
Alternatives: "an extensive introduction" or "a lengthy introduction".
A long introduction announces a work of grand dimensions.
Weiss was given a long introduction by Robert Vessot, a straightforward nuts-&-bolts type of physicist.
For a long introduction to the title track she plays completely unaccompanied.
It includes a long introduction and countless footnotes that point out the many flaws in Hitler's arguments.
The whole book was preceded by a long introduction and concludes with a poem praising the ideal wife.
A long introduction with the violinist Curtis Macomber playing glassy harmonics at the top of the fingerboard had the charm of a dentist's drill.
We did not want to write a research article with a very long introduction, but preferred to formulate a hypothesis and then (after some studies) write a concise research article on the subject.
His first publication (1962) was a very long introduction to his translation of a short essay by Husserl on The Origin Of Geometry.
Chapters 1 to 3 (pp. 1 61) seem to me a long, long introduction collecting disciplinary justifications, theoretical definitions, broad general claims, a brief history of taxonomy, a survey supporting devolution a concept that in my opinion only becomes clear in Chapter 4 and other sub-arguments.
After an overly long introduction that included a peppy video extolling Mr. Lacombe's virtues, and onstage remarks by symphony administrators about fund-raising successes, the concert began with a taut, vividly rendered performance of the Overture from Mozart's "Marriage of Figaro".
The song begins with a minute long introduction sung by Legend.
