Growing up I played two types of games.
There were true sandbox games, such as The Sims with no real beginning or ending. And then there were games with a point. The games with final goal, a point to reach where you could say you had finished it were usually around 25 hours if you didn't know what you were doing or as little as 16 if you did. Some magazines-- Looking at you Electronic Gaming Monthly-- would call these "short" but the truth is that it was short for an RPG compared to, say, the Final Fantsy games of the time but pretty standard length amoung other games that were less story-oriented.
The question, then is How long do you need to play a game to review it?. I've touched on this idea before but No Man's Sky-- bless it-- has fans saying that 20 hours isn't enough time to form an opinion on it. The game, apparently, takes more than that to really pick up or something. Now I would go out on a limb here and say that if the games not pick up until after 20 hours in but the game does not make you actually want to play that long then surely it has pacing problems?
Think about the Lord of the Rings films-- they're long and not everyone likes the length. The length works for some people becase they don't feel the film is paced too slowly. I am one of those people who feels they are too long.
I have seen fans blame society or attention spans to defend something they like. It is really an attention span issue? I mean I've read one of my favorite books The Unbearable Lightness of Being three and a third times now. I've happily read through very dry government documents of hundreds of pages just fine. Surely I don't have an attention span problem? So then why do I not want to sit and play a game for millions of hours? Maybe the games just aren't that good. Maybe in that time I've seen everything there is to see and done everything I want to do?
Maybe pop culture creates a false impression that media can be objectively good or bad?
Nah, I'm sure there's something wrong with my brain chemistry. Same thing that makes me not like sports or Game of Thrones, probably.