I do agree that game reviews are pretty busted. You have a mixture of star system, out of 10, or out of 100. Some outlets see 5/10 as average... But most don't.
With films for example there's a widely used 4/5 star system. It's easier to gauge what a score actually represents.
But reviews are rarely "fair". They are generally subjective. But I don't really mind, I quite like scored reviews. I have more issue with, say, the Rotten Tomatoes system where a thoroughly average film can wind up with a very high fresh score. That to me doesn't do a good job of representing the quality of a film.
I also think it's kind of amusing that you don't think that a games average review score should be compared to other game reviews because it's not fair... But also insist that 80 is a great score. Reviews are intended to rank things relative to other things in the same field (ie; games). You're saying that 80 is great relative to what exactly? What an 80 represents in other fields? Ehhh
You can go with the approach that reviews aren't intended to rank things, and should really just be used to get a baseline on whether something is recommended or not. That's a valid approach, and many are moving away from handing out scores. But if that's the way you see it... Review scores shouldn't hold any weight with you at all. So the natural reaction would be 80 = generally positive reception. Not 80 = great scores!
All I'm really trying to say is that I think it's inaccurate to say this game has had a "great" critical reception, and some people are overselling it. For the record, I think that ultimately this game will be viewed as quite a bit better than the last 2 entries. But that doesn't mean it received great reviews.