Why can't you compare them?
Also, if a game is 30 hours long and starts to drag after the 20 hour mark, do you not think that game could be better if it were 20 hours long instead?
Yes, of course. But in this case, the game is boring. The gamedesign is flawed and in itself a negativity, that overshadows the length. It is the responsibility of the dev to ensure that the game does not get boring imo.
Again, assume the game does not suck and is boring, assume it is good: when is it positive that the game is short.
Assume the game is shit, there is imo no need to discuss its length.
Assume the game is good for 20h, and boring the last 10h...it is not the fault of the 'game length'...it is the fault of bad game design.
A game does not automatically turn boring when it is long. Thus, it stands: short length is an objective negativity.
You cannot compare movies and books: they only deliver a story, no sort of interaction (gameplay). And the price is also different.
And, where I live, the movie length indeed is reflected in the price you pay for the ticket: if it is a long movie, it costs more.
The problem is imo the ratio of typical expected length to price. It seems that the order (apparently 8h long or so for 60€) is not very good in this regard.