I have read The Moonstone at least four times, the earliest of which was when I was an undergrad. I had been assigned Collins' The Woman in White in a Victorian Literature course. It was so enjoyable that I read this one too. Since it had been years since my last reading, I added it to a reread challenge I am participating in this year.

The Moonstone is largely considered to be the first detective story. Told through the written accounts of multiple characters in the story, the mystery of a missing diamond unfolds. There are likable characters, despicable ones, insufferable ones, and clever ones. Despite being rather long, it maintains interest and the plot moves. There is some subtle social commentary (society and class, gender norms, imperialism). 

This is a book that I know I will revisit in a few years.