While the whodunit/mystery aspect still was somehow interesting, I was much more interested in the character studies. Wilkie Collins created wonderfully fascinating, quirky characters that represent perfectly some types of people everyone knew at the time and in a way still knows now. My favourite example of the relevance of this portrayals is the butler, whose obsession, excapism to, and almost religious believe in the book Robinson Crusoe is a better caricature of modern fan culture than anything you see in contemporary works.
I loved how every different point of view changed and shaped the readers thoughts on the characters, especially Rachel. Also, the framing devise of the book being a collection of accounts about the case was quite clever and well done. Above all, the good balance of humor and serious topics and moments was outstanding.
It had some adventure, some love story, some mystery and satire, showed the thoughts and lives of different classes and all of this in a really nice writing. It deserves to be a classic.

I think 4.5 stars comes closest to the rating I want to give this but since there aren't half stars at goodreads I'll settle for 4. It's just not a perfect 5 stars for me since the mystery itself isn't as intriguing as others I loved, but I might still change the rating.
(Edit: What the heck, I'm just giving every book that "feels like a 5 star" to me the appropriate rating now. Critique still stands, and that's ok.)