I knew/know almost nothing about Dickens or Wilkie Collins before reading it which may have helped protect me from what you're experiencing. You're guess about the narrator being untrustworthy is a good one

I liked it from an atmospheric standpoint. I'm not a stickler for really good writing if I'm being entertained in other ways. I found the language fine. I literally felt sort of grimy after reading the book, so thick was the imagery of the setting and the less than scrupulous behavior of the characters, etc.

Like I said, maybe being ignorant of the subject matter in this case was perhaps a good thing for me as a reader. In any event, I enjoyed it.