Like Firebolt said up above, I use the ratio 1 euro to 1 hour of enjoyment as a general rule of thumb for me. Although this makes me incredibly hesitant to buy AAA priced games, I feel it generally does pay off whenever I adhere to it. Of course there are games where I've spent over 300 hours in them (LoL and Rocket League) and enjoyed my time thoroughly, though I'd never spend that much on the game, whilst there are games like Stardew Valley where I think I spent like 15? on the game but have barely played it. So it doesn't always work out but it saves me a ton of money in the long run, money I need to keep saved right now as it is lol