I have a rule I refer to as the pint limit.

If you are in a pub and have one pint an hour, you would generally consider that to be a good use of time. This means one hour is worth approximately the cost of your usual pint at your local pub. For me this is about £3.50.

I then divide the price of the game by this number to get the number of hours the game has to provide to make it worth it. So for example Risk of Rain 2 cost me about £21 and I have played about 280 hours, meaning that I have exceeded my pint limit of about 6 hours by nearly 274 hours. Solidly worth it!

Occasionally a game will not reach its pint limit, but will be worth it nonetheless, e.g. The Return of the Obra Dinn, but generally I find the metric exceptionally accurate to my feeling of worth for a game.

The final advantage is that this scales with the cost of living (and usually thus wages) in your area.

I think about 10% of the games I bought since 2016 have not yet reached the pint limit, which is generally pretty good going.