And where's this neutral, objective standard by which these people's opinions can be compared? How can you figure out how good something "really is", separate of the majority's opinion of it?
Let's take the example of Call of Duty Modern Warfare 2.
It is the most overrated game in gaming history.
Not to say it is a bad game, even though I think it is, but it really is overrated.
So how can I know this by neutral and objective standards?
Let's look at what it offers. A First Person Shooter with below average graphics for that time (Many games were HD by then, which Modern Warfare wasn't), gameplay strikingly similar to the basic gameplay of many other modern-war time First Person Shooters not just of that time, but even before then, with little extra to offer besides kill streak bonuses. It's maps were small compared to other less successful shooters and it was unbalanced.
It was sold at a standard AAA price of 60 dollars/euros, or whatever, although most of it was unoriginal or subpar for that time.
I think it got a 10/10 in most magazines and got praised as Game of the Year, or potential GotY.
That, my friend, is overrated.