Games offer all sorts of experiences. Some are suited to short narrative based structure and others have open unlimited structure. To me if I enjoy a game and feel I got good value then I am happy. I know what I enjoy and adjust how long willing to wait on price drops and sales accordingly.

When you get a bit older money actually isn't the thing that stops you from buying games, it's the time available. For example recently I completed Fatal Frame V Wii U and enjoyed the game but also liked the fact that after about 15 hours or so it was over. That is a good length for my current lifestyle.
Now of course there are exceptions. A game like Zelda, Xenoblade or Fallout etc are games that would take much longer than that but the game is so good they can maintain your interest for that length of time but there are only a couple of these games per year that I can find the time for.
I do agree that a premium AAA game at full price can't be too light on content, but it's the experience not the length at the end of the day.
The best movie I saw in 2015 was Gravity 3D and although it was only 91 minutes long it had a much greater impact on me than any 3 hour epic in recent memory.

Its nt an issue as long as the game is good, i could play Bloodborne forever cuz tge game is that good

Long games are fine, but I need to, you know, be able to eventually finish it and be able to start a new one within a year.

That's really not the issue, per say. But when I beat a game, within the same day I bought it. That's not acceptable. That's why I don't see a 5 hour game worth $60. If it was less, yes. I'd prefer all average games to be around 15 hours. And that's the main story campagin only. None of the side missions/DLC missions are counted towards this. 100 potential hours is fine. Pokemon games are potential games. They last around 10-20 hours. But you can play it continously to reach 100 hours. Which is good & optional.

When the game starts sucking or when it isn't good in the first place.

I rather have the game end before I get tired of it. TW3, great game, left a bitter after taste. Instead of being glad it's finally over I rather feel like starting another playthrough or replay certain parts. I did 2 playthroughs of Infamous SS, the length of that was just right for me. The problem with long openworld RGPs is that you're petty much done building your character long before the game is over and levelling up becomes very slow and pretty much irellevant. I know when I'm tired of the mechanics when I stop looting.

It really depends on genre, replay value, full completion fun factor, etc.

For instance, when I played shooter games back on the PS2, I was perfectly fine with a 6-8 hour campaign, which I may never play again, but it had fun local multiplayer.

For a game like Mario, you can obviously just cruise through, but it is about enjoying all the different stages put together, gathering all the collectibles, and they tend to be very fun to play with friends, etc.

I had issues with Dragon Age Inquisition because i felt it was too long, i became disinterested around 75 hrs or so. Thays the primary reason i have not taken the plunge on fallout 4. Then theres the other side of the spectrum if you can complete it in one sitting cough the order cough then thats an issue as well.

Pretty simple really

Length is an issue when I finish the game and say "that's it.....?"