Most of the times I compare my purchases of video games to movies. Granted I don't go to the movie theater anymore but I like to compare them. If a movie cost around 10 dollars to see at a movie theater for about 2 hours entertainment then if I can get at least 5 dollars (or less) per hour of gaming in for the game I bought then I feel like I came out ahead. So for a 40 dollar game I hope I to play it/have a good time for at least 8 hours. If I don't get at least 8-10 hours out of a $40 game then perhaps it wasn't worth it.