When Darwin wrote this book, probably to be read at the Royal Geographical Society, the Victorian age was in its childhood and hunger for information on faraway lands was at its peak. So that's why he extends in descriptions more useful to naturalists than to common readers. I would however recommend its reading, jumping perhaps over the naturalists' paras, because the author's eyes discovered and preserved in text many other local details and people's customs, now disappeared, that can answer many of our today's questions about the countries he visited. I'd give it a B+ mark.