£1 per hour in a story driven high quality game with little to no replayability.
£1 per 2 or so for an RPG type game, mainly because they get abit copy pastey to fluff out the content so you expect them to be long, and rarely have huge quality to them (god bless Witcher 3 - a true standout of the genre)
Multiplayer driven games like Tekken CoD etc. probably expect 80-120 hours min just because they generally don't have that much new content with each release and are quite confined in what you can do, but highly replayable.
Hard to say for the rest, ARK having 2400 hours for me is mental though, at £25 that's what... 1 pence an hour? Lmao. Though for the pure sandbox games with no structure like that, you'd probably want 200+ if it grips you by the time you're done, just because they're quite easy to pile up content without much thought.
Hard to say honestly, but it's very difficult to justify less than say 40 hours of good content for a £39.99 title, which puts pressure on developers if we're honest especially with time constraints. Not hard to see why so many developers just cave and make their games open world pseudo-RPGs now, it's very easy to fluff the content out so people feel like they have value from their purchases. Even games like Evil Within and God of War are going that route even though they had highly repayable content despite being linear.