I'd say playing around 4 hours is enough to get a general impression of a game's quality. If the story was ridiculous after 4 hours it's a safe assessment that it's not going to be good after 10 or 15 hours either.
As for the other issues: does the game not have framerate issues? Does it not have a shitty camera? These are issues of which you can obviously get a good impression, even in very little playing time. I have not played the game, so you tell me.
Furthermore, they praised certain aspects of it, such as the art and the voice acting. I'd say they were pointing out the game's flaws, not entirely dismissing it as the worst game ever. What went down on the stream was just their opinion, not a full-blown review.