I've never timed the amount of hours I've put into a game. It's always been about my enjoyment of it. 10 hours of boredom vs 80 hours of enjoyment, or 10 hours of enjoyment vs 80 hours of boredom...I'll take enjoyment every time.
I agree, but the problem is when the early hours are fun but later hours lead to boredom. This can happen for some really long games, and many players (like me) are too stubborn to simply stop playing when they get bored. So sometimes it's nice to have an estimate of the length. Also, sometimes players are in the mood for a certain length experience, either looking for something quick to fill a bit of time or ready for a real long haul of a game. Knowing the approximate length ahead of time can therefore help players decide whether they want to play the game now, or wait until later to play it.
Fortunately, I never found myself bored with the Geneforge games, so the first concern is likely moot. Unfortunately, I am terrible at estimating how long it took me to play a game in hours, so I can't really help respond to the second concern.