I think it's kind of missing the point and it's a bit reductive to say the word has nothing to say. It does, if explained properly.
However, 'overrated' may also be reductive if not explained properly. People need to think about what they're saying and mean what they say.
I see your point, I understand where you're coming from. The problem isn't necessarily the game itself, it's more about the fan base which may exist in kind of an echo chamber.
It means the poster thinks people give something too much credit, that it may receive a disproportionate amount of praise. You can still love something and say it's overrated. It's not mutually exclusive.
For instance I love Half-Life 2 as much as the next guy, but...GOTG? GOAT? I can't say that in good conscience when the game has so many huge flaws. Really, I love HL2, but it's still a huge disappointment to me. In a way, it's a testament to how good it is, to overcome such hurdles and make it out so good. But HL2 has fundamental issues that I can't ignore, that I feel most people do, for whatever reason. Yes there is looking past flaws in a game, but I don't see people even admitting these flaws. That is a key point when it comes to something being overrated, when everyone seems to overlook or downplay real issues. And I don't mean nitpicks, I mean something that adversely effects the entire experience in a negative way.
I love using that word. I think it's great.
However, everyone will have their own opinions on what's over/underrated, but they need to come prepared with opinions that carry weight. 6/10 too much water isn't a good opinion unless backed with substance.
It's all about reception, commercial and critical, and overall consensus. Think about games you hear a lot about. Games you hear nothing about.
Halo? Destiny? IMO, massively overrated. Turok 1 and Doom 64? Massively underrated. It's all about if you think you hear a disproportionate amount of praise or a complete lack of praise for a game.
I will continue to use that word when I think the case calls for it, sorry.