Of course it does, the core gamer is swayed by "what's popular and what's not", and that also plays into what they think about the games, but I can't say that every game that is overlooked is underrated. Similarly, I'd agree that overlooked games can be overrated, because they still have a fanbase, even if the game itself is crappy, that much is true.
And yes, something can be overrated compared to something else, but I, like many others, don't use comparisons to determine if a game is good or not. I determine it by how good I think it is as game by itself. You don't need another game to determine if a game is overrated/underrated, you just need to have a good idea of what you consider is a good game (sure, that "idea" is formed from playing other games, but you're not comparing the games themselves, instead you're comparing the games' concepts, features, and what you take from the games subconsciously collectively to form your opinion on gaming as a whole, rather than seeing what the game does right relative to other games individually). You don't need to compare it to other games (though some people only do that), you just need the experience to determine what you personally believe makes a good game. Sure, I could say that one game is rated high and another game deserves that rating when the former game doesn't, but that doesn't determine which game is overrated and which is underrated; it can't, because the person who was thinking that was comparing two games, one they considered overrated and one they considered underrated, they decided that before they made the comparison. They decided that one game deserved a lower rating and one that deserved a higher rating first, then compared the two, nothing more than that. It's simply a comparison, not a determination which one is overrated or underrated (unless one person forms opinions through comparisons, in which case it is a determination). It really all depends on the person and how they form an opinion on something. (which is why I have a love-hate relationship with the subjective world we live in).
I don't think I ever said that they said it was bad, just worse than the person who is looking at the general consensus' (or critical, it's objective) opinion thinks it is. If I did say it, it was probably by accident, but it might have just been a poor choice of words.
Also, there was a 4 minute gap, but I didn't think you'd start reading it the moment I posted it, and then post a rather wholesome post yourself in that time, that would be a rather extreme prediction that I definitely wasn't ready to make.
One last thing. I don't think that it's really fair to say that something is underrated or overlooked if someone forms an opinion about something yet don't make it publicly known. I see what you're saying, people do indeed form an opinion about something when they decide to look it over, even if it's not their final or full opinion about the item in question, but I don't think it's really the right thing to count those that have not publicly voiced that opinion. I don't really think I can say what my opinion about this is because, really, I've never even thought about it, what I'm saying now is on the spot, so I don't really think I can back it up or reinforce it (it requires more pondering on my part, though I am grateful that you've raised this theory, it's something to think about).