My review of Paradise Lost was not wholly positive, to be sure, but there were parts that I loved, and the other parts were still good enough that I could see why the whole thing is such a big classic.

Certainly, sometimes people truly hate a book that is considered to be a classic, and have their doubts about that status. But it's not as if all "classics" belong together in some sort of genre which appeals to some people and not to others. "Classic" is merely a quality label, a term used for books from any genre that are considered very good. If you really hate a particular classic, then perhaps that's because you're not fond of the genre, or the subject, or the writing style; but it doesn't tell you anything about how you'd like other classics in other genres, on other subjects and with different writing styles.

So when people just feel a lack of interest in "the classics" in general, that's really a shame because while they doubtlessly have their reasons for that, having read some and disliked them, there are bound to be a good number of "the classics" that they would like, the trick is just to find the right ones to read.