I do not personally believe that using a formula that equates your hours to money spent is an effective way to measure the quality of a game or if it's worth your time. I have enjoyed lots of short games and enjoyed lots of long games, but I've also been disappointed by both short and long games as well. For example, I played through The Last of Us once and enjoyed it even more than I enjoyed playing an open world game like Watch_Dogs. On the flip side, I was a bit disappointed by The Evil Within and didn't even finish my playthrough, whereas the open world of Shadow of Mordor kept me coming back.
Every game tries to do different things in different ways so just because its length might be short when compared to a game in a different genre, it doesn't necessarily mean it's not worth the money in my opinion. I feel like gaming has evolved to be too complex of a medium to simply water it down to "how much did I pay per hour for this experience?"
But hey, we all judge things differently and that's what's great about games!