According to my wife, Wilkie Collins is by no means second tier.
I think he's second tier in the sense that he was friends with Dickens and there's a discernible difference between them. Only one is Dickens.
But I really liked No Name, a terrific ur-feminist drama that would make a great movie (especially if you improved on a somewhat weak ending). Two sisters get screwed out of an inheritance by a quirk of the law, one sort of sinks into being a governess with no dreams of her own, but the other... Edmond Dantes has nothing on her.
* * *
Speaking of high school reading curricula... as the father of a newly minted graduate, I'd say that the curriculum is definitely skewed more toward "diversity" these days, but generally of a high caliber-- I mean, if you read Native Son and To Kill a Mockingbird instead of Huckleberry Finn and David Copperfield, I'm not going to say you had a markedly inferior experience (and we'd already listened to Huck Finn in the car on the way to school, years ago). In any case, I know my son had to read The Scarlet Letter (hated it) and the ever-present Julius Caesar as well as some YA Fiction type books which are not classics, but worthy enough for discussion in class. On his own he asked me what the greatest book ever was, and I said The Brothers Karamazov, and he's about halfway through it. When he's done I'll tell him I lied and it's really The Red and the Black, and he can read that next.
As far as punitive reading, my hands-down Hated, Hated It book is The Faerie Queen which, thanks to an old school education, I was subjected to in both high school and college. The hardest slog of a classic which I nonetheless finished was Willa Cather's My Antonia.