Y≥X/.6, where Y is the number of hours of gameplay you received from said game and X is the amount you paid for a game in dollars, rounded to the nearest 5.
This is how proper games are made. Typically by Bethesda. A $60 game should thus give you 100 hours of gameplay, which is definitely seen in Fallout and The Elder Scrolls saga. I haven't beat Just Cause 2, but I'm at 14% and have 15 hours logged, so I think it's going to be pretty close. That is all.