First, a word about the Kindle file (which does not influence my rating). Every few pages I would get an error message that would throw me back to my home screen. The only fix was to download the file again from Amazon, which got me a few pages farther along. I tried to return the product, but I was unable to do so, nor to make contact with Amazon over the issue. It's only $0.99, but it's still annoying. I ended up finishing the book from paper copies.
The stories move far too slowly for modern tastes, filled with pages of trembling emotional reactions to everyday events that quickly become tiresome. The books were originally written to be serialized in magazines and it shows. Each section begins by resetting the scenes and resolving the cliff-hanger from the previous section, then there's lots of going to and fro and characters telling each other stuff the reader already knows, before a not-very-thrilling cliff-hanger to end the section.
The plots themselves all involve young love, crimes from the previous generation, complex inheritance rules and worries about money. Although these kinds of stories were popular in mid-Victorian times, they were 100 years out of date in most respects when published. People do take trains now and then, but most of the transport is walking or horse-drawn. No one sends telegrams or sees a factory. No one has a job or interest unfamiliar to prior centuries. The social structure is thoroughly Georgian. Near-universal literacy seems to be assumed, but in other respects worldviews seem little changed since the 18th century.
Characters are broadly and humorously drawn, but do not develop. The mood is all imposed by the narrators. Descriptions are pedestrian.
I find it odd that people identify The Moonstone as the first detective novel. Collins' earlier The Woman in White is a more conventional detective story, and there are many similar earlier examples of romantic novels with puzzles at the core and characters who steadily unravels the truth.
But all of these lack important features that were supplied in Arthur Conan Doyle's Sherlock Holmes stories and later works. There is no concept of playing fair with the reader, or of clues revealed to the detective and the reader at the same time. Crimes are not solved by either logic or psychological insight. There is no concept that the facts force one solution, nor that there is a single core solution that explains everything. Lots of loose ends remain at the end. These books are romantic novels with puzzling events and crimes that are eventually explained--and that the reader usually figures out long before the characters; not by logic or insight; but by figuring out the author's style--not detective stories.