Wow, what? The reason people don't ask how long a movie is is because they don't need to ask; for the most part movies are fairly consistent length, in the neighborhood of 2 hours. If I went to the theater and bought a ticket expecting a full-length feature film and instead got something 45 minutes long I'd be pissed the same as if I bought a video game for 60 bucks and it was over in 4 hours.
So the issue is perception and not if it's actually worth your money or not. Got it.
What does that even mean? The only issue with any kind of consumer satisfaction is what they perceive. You're right, I will be unhappy if I perceive it to not be worth my money, because that's the only way to determine if it was worth my money. There's no objective way of determining that.
That said, just saying I'll be pissed if the game is short and leaving it at that is an oversimplification. I liked Journey and it was short, but it also didn't cost $60. And obviously a bad game that's 70 hours long isn't worth anything to me, because it's a bad game. The question is how much enjoyment will I get for my money, and if I enjoy the experience of playing the game (as in the moment-to-moment gameplay) then making the game longer will add to the value of the game and making it shorter will detract. As dean likes to point out, people make a false dichotomy between short good games and long bad ones, as if those are the only options. Long good games do exist, and have more value (to me) than short good games, because I get more enjoyment out of them.