I don't consider my gaming in terms of price/time because that just encourages buying games that suck away my time.
My value for gaming is less of a simple equation, but my examples of games that are "undoubtedly worth the price" are going to consist a lot more of shorter games that are absolutely spectacular for their shorter playtime with a £30ish price tag.
Think:
- Outer Wilds
- Tunic
- Hollow Knight
- Journey
- The Witness
- Portal (1&2)
- Celeste
- Undertale
- To The Moon
- Ori and the Blind Forest/Will o the Wisps
- The Witcher 3
I have no strict criteria for this, but I can say I've had far, far more than my money's worth from those games in terms of the value they brought to my life.
If you do want to look purely at the number of hours you'll get out of a game vs its price, look no further than Guild Wars 2. You can get all the content for under £100 I beoieve, and I've spent 6000+ wonderful hours playing it. It's not the same kind of enjoyment though.