If I've said it once, I've said it a billion times: "overrated" and "underrated" are entirely subjective terms and thus utterly irrelevant to a discussion on quality.
Isn't quality itself subjective?
Partially, but not entirely. There are certain things that are demonstrably objective. To make an extreme example: no matter which way you cut it, 'Rise of the Planet of the Apes' is a quantitatively superior film compared to 'Battlefield Earth'.
The idea that anything is over or under rated presupposes that there is a fixed point, or consensus at which something (or indeed anything) is "rated", which is just spurious nonsense. What person really means when they say this is "I like/dislike this thing more/less than an arbitrary group of people."
It's mostly just an excuse to feign a controversial opinion. As if having a differing taste is something notable.