"German literature of the 18th century emerged not from the imitation of works of the English empiricist Enlightenment nor from Gottsched's Leibniz-Wolffian and France-oriented rationalism but from the conflict of the two, a conflict which mirrored the diverging interests of the official and the bourgeois wings of the German middle class, and which intensified as the century wore on."
This is clearly an over-simplification, but it provides a framework around which newcomers can organise what would otherwise be a mass of details. It also helps avoid the banality which a more encyclopedic survey of this length would have risked.
The bulk of the Very Short Introduction consists of long, "German style" single paragraphs, covering a subject rather than a single idea. These are typically around a page or even a bit longer, and focus on individual writers or poets, often on a single key work, or on broader themes.
The coverage is dominated by "the two distinctively modern literary genres", subjective lyrical poetry and the objective realist novel, but it extends to other literary genres and even to inextricably interwoven aspects of philosophy and history: Strauss' Life of Jesus, Wagner's operas, and so forth. Boyle's evaluations sometimes seem to mix political judgements with literary ones, which can be jarring.
Boyle omits any treatment of the medieval period or Swiss and Austrian/Hapsburg literature — so there's nothing on Kafka or Rilke, or on Dürrenmatt or Frisch — leaving those to three additional chapters available on the Web. Even with that reduction in scope, many important themes and writers are necessarily omitted.
A Very Short Introduction is not terribly useful as a reference, obviously, but it's good fun to read and should work to provoke an interest in its subject; there are two pages of further reading suggestions for those who want more.