With each chapter he delves deep into some aspect of intellectual life - about half the time it's theology, where Buncle (and presumably his author) have very strong Unitarian views, and one can more or less tell whether a character is good or bad depending on their attachment to the Trinity ("it is a word invented by the doctors, and so far as I can find, was never once thought of by Jesus Christ and his apostles"). But the other half of the time it's natural science, and the author's ability to reshape the latest scientific information into readable form is pretty impressive (though a novel is not where we would present such information today). There are particularly good sections on geology (with deep anxiety about the Abyss) and what we would now call the chemical elements. It's all heavily footnotes (I counted at one point a third level of annotation, footnote to a footnote to a footnote).
Although Buncle starts in Dublin, actually most of the book is spent exploring the wildernesses of Westmorland and to a lesser extent North Yorkshire, with excursions elsewhere (he stays in London with Edmund Curll, who was a real person, and encounters various other real people too). The landscape secriptions are particularly good. I can't really recommend it as a novel, but it's a fascinating case of what happened when an eccentric eighteenth-century gentleman sat down one day and decided that he was going to write a story.