No matter how great a piece of fiction is (or anything else made by humans), someone out there is saying it's overrated.

"Overrated" is an overrated comment. "Overrated" according to who? You mean you don't like it as much as others do. Ah. Well why didn't you say so? It sounds so much less pretentious when you tune up the accuracy of your statement.

I'm almost always a little dismayed by the attitude of people who will approach something that has succeeded wildly, who will try it out, not like it much, and then prance about calling it "overrated" to anyone who will listen.

I suppose it might be. But why would I trust your judgment on that unless you're showing other signs of good judgment? And in fact, why would I trust your judgment on that? No matter how classic, there will be plenty of these naysayers. They never seem to notice how predictable and unmeaningful their presence is.

Why are you so sure that you got everything out of it that's in there?

Why do I so constantly find myself grasping works and their strengths and weaknesses far better than what these supposed connoisseurs display?

People say "overrated" usually to excuse themselves from making further effort. Only very rarely is it the conclusion of exhaustive analysis. On the contrary, it's a sloppy self-congratulation. Everyone else thinks this is great, but you know better, you intellectual slayer, you.

It's almost comical how easily people fall for their own weaknesses, thinking those weaknesses belong to someone else they're talking about.

By all means criticize. Just try to do so intelligently and with a little humility and open-mindedness.