I think the package as a whole is quite overrated. I for one did not find the game play particularly satisfying, mostly due to the fact that through Materia character appeared to be not really important. Toss a Long Range one on Cloud and boom, he's essentially Barrett. Maybe I missed it but aside from weapon options and Limit Breaks there seemed to be very little differentiation, and even those eventually fall away as meaningless. I felt more that I was building Materia sets and then just throwing them on whatever character I liked more rather than picking a party based in strategy of any kind. Doing this the game presented little to no challenge throughout, even without any grinding on my part. I also feel, unlike others, that the music is not overall anything spectacular. I blame this solely on the teams unfamiliarity with the Playstation hardware more then anything else, but the point still stands that I often found the music droning or annoying. I feel I have a pretty good grasp on the story, having played through the game twice and read up on it a bit to see if I missed things. Knowing what I do I would definitely say that it's decent, but hardly anything to write home about. The fact that I thought this only after learning things through other sources that I missed through two full playthroughs says something to me about the original games storytelling.

Anywho, getting to the question I guess I would say yes, of course something can be over and underrated. Anytime two parties disagree on something both will likely feel one way or another toward whatever that thing is. I think that Half-Life 2 is overrated because I have not been able to get into it. Does the fact that it has millions of fans mean I am wrong? No. Likewise, if someone feels that FFVII is underrated despite it's critical acclaim and large following then it is, to them at least. Both terms are purely subjective, so they can both exist regarding any given thing.