Since both the skillset and amount of free time the player has is unknown, it's difficult to quantify the amount of entertainment a game should contain. Two hours of fun, or thirty hours of boredom, tediousness, and frustration? The question is too vague and broad to nail it down to dollars and cents per hour. Some cheap casual games can give you endless hours of enjoyment, whereas a high budget $70 game can be played through in 6 hours, with little incentive to play through it again. Once people wake up and realize they don't spend $60 on a DVD or a book, we're in trouble.
J Kelly, Sea Cow Games
It's a fine balancing act. Making a game very long limits its audience or simply wastes development effort, since only hardcore gamers will put in the time to complete very long games like Oblivion or Zelda. On the other hand, a game's critical reception is hurt if it is too short. Many good recent games, such as Gears Of War and Dead Rising, take an effective tangential approach to addressing this issue - they provide a game which is quick to 'complete', but they encourage replay by adding secondary objectives that you won't fulfill first time through. This seems like a good model to follow, as it allows developers to focus on a reasonably sized core experience, while adding value by layering lots of hidden goodies and unlockables on top of it, and by structuring the core experience such that replay is rewarding (e.g. through Gears Of War's finely honed difficulty settings). While it may only be catching on recently, this idea isn't new - StarFox 64 is an excellent example of a game from the past that did this really well.
Iestyn Bleasdale-Shepherd, Electronic Arts - Tiburon
I would say as a gamer on the more casual side (30+ years) the game length is fine around 20-25 hours. If you are having fun while playing. I never have time to finish anything longer. It makes me more satisfied to have played through the game in 20-25 game hours than never even reach half way.
Joachim Carlsson, Massive Entertainment
I've got a 16-month-old son with another on the way, so two things I don't have much of are time and money. What I want is a choice of short, mid-price, high-quality games. I'll avoid high-price games where I'll never see 50% of the content I've paid for, and won't finish it. Half-Life 2: Episode 1, God of War, Fable, and the recent Prince of Persia games were a good length. I'm actively turned off games advertised as very long. Final Fantasies, WoW, Baldur's Gate, Oblivion... all games I'd like to play, but I won't, because when I start a game I want to finish it - which by my definition means getting to the end credits (except racing games, where I'm happy to play it til I've had enough - which makes them a draw for me). I don't need to collect every figurine, grind every edge, find all the hidden magic badgers. If I don't think I'll be able to do that, and these days that means the game should be 10-20 quality hours, I probably won't buy it.
I'll make an exception in rare cases - I'll find the 60 hours for Wii Zelda one way or another! Worth noting that handheld games are a slightly different matter. I play them on my daily commute, but at an hour a day I don't want to be playing one game for more than a few weeks. And they're cheaper, so a good game (Zelda: Minish Cap right now, Mario Kart DS... in fact just about anything on DS) is a great value proposition. Finally, if I've grabbed an hour while my son is asleep and want to play a game, I want to make progress - I don't want to play the same difficult ten-minute stretch six times. I feel like it's a waste of time. I'll always look for an Easy setting. Oh, how I miss having whole weekends free to play games... although, having a wife and kid isn't a bad alternative!
Ben Board, IR Gurus Interactive