When you take out the politics out of To Kill a Mockingbird, it's just a story about two kids being curious about their surroundings and questioning it.
Lord of the Flies is just about some kids stranded on an island subjected to darwinism and lack of parental supervision.
The kind of people who leave one-star reviews are the ones who don't get the significance of these classic works. They read it like any other modern piece of work and apply it to today's standards. There's also the problem that people read these books after reading all the others that derived from them, this causes it to be the "same old thing" and "boring".
If you can't comprehend the material, you might consider extending your education in the English language, including seeing how it has evolved over the last 100+ years. That and a good dictionary and a few encyclopedias.
Too far? Better than to say you lack the knowledge and should just not bother to try to read these books at all.