The adjectives are not technically sentences, but are written this way (with a period after each) informally for emphasis.

Would you prefer that the author write grammatically correct sentences like this His work was horrible, they said. His work was crude, they said. His work was disgusting, they said. His work was depraved, they said. Doesn't this sound very boring?

It's used as a stylistic tool to put emphasis on every single adjective. It makes it feel a bit like: "His work was not only horrible, but also crude, disgusting and depraved."

Authors often take liberties with grammar rules for stylistic purposes. The last three adjectives modify the noun "work" in the previous sentence. This is obvious to anyone who understands English, so it's not necessary to repeat the noun or construct complete sentences.

From what I see, its written this way to emphasis how horrible the work is. The writer is piling up the words. You can also imagine it as just switching the word 'horrible' with any of those others words. It is horrible. It is crude. It is disgusting. It it horrible. Crude. Disgusting. Hope this helps somewhat! :)