It really only takes a couple hours to beat Super Mario Bros, but we all played it way more than that. If a new game came out that delivered the greatest gameplay ever imaginable, yet it was one second long, I'd buy it, and if it delivered on that one second, I'd be happy.
Tony Dormanesh, Collision Studios
There's a lot more involved in a game's value proposition than just the number of hours of gameplay it provides: consider factors such as richness of content (Gears of War), conceptual novelty (Beyond Good and Evil), or a creative (as opposed to destructive) approach to gameplay (The Sims). The idea of "hours per $ purchase price" is fundamentally silly to me because there are equally-worthwhile games at both ends of the play-time spectrum. Unlike film, our industry need not adhere to an accepted "standard length"... it's one of the very celebrations of gaming that you can have as much fun in 10 minutes as you can in 10 hours. Wario Ware, anyone?
Josh Sutphin, Incognito
I often don't buy games I'd love to play because reviews mention they're 70+ hours. I don't have time for that kind of commitment, and I don't like buying games I know I can't finish. That said, it really depends on the genre. I can play an RPG for 40+ hours, but I don't want an FPS to be 40 hours. There is a point where I wouldn't want to spend $50 for 6 hours of mediocre entertainment, but rarely have I been disappointed with a game because it was too short. It's almost always because it wasn't compelling, or it was buggy, or had poor game mechanics, etc. What I really want is a fun and memorable experience that keeps me engaged and thrilled all the way through, regardless of raw length. I finished Shadow of the Colossus in three sittings, and it was one of the most memorable games of the year.
On the other hand, I can think of more than a few games that would have been a better experience with a few hours trimmed off (thinking "when is this going to end" is not particularly fun). What makes the most sense design-wise is where more game content is available to the players that want it, but not mandatory for those that just want to get through the mian game. Skies of Arcadia did a fantastic job with this by providing optional side missions, seamlessly integrated into the main quest. God of War had extra levels for hardcore players. Resident Evil 4 had bonus missions and game modes. But all of these were completely satisfying for an average player who wants to just play through once.
Vince Dickinson, EA-Tiburon
It's depends on the genre for the most part. A shooter is typically around 8-10 hours while an RPG can quite literally be a game that never ends. In the end it comes down to what the developer feels is appropriate length for the fun and design concepts (both new and old) that the player will enjoy. Something like Okami is a massive, long adventure that takes a long time to finish just due to sheer length, not necessarily challenge--they could probably taken out 1-2 areas and had little impact on the game experience. Whereas something like Resident Evil 4 has excellent length for both gameplay variety and story development. An hours per purchase price for a console game would backfire, as essentially that's a mini micro-transaction game, level by level. Who would honestly have bought every game function of Lumines? Or a Halo that charged per multiplayer mode? That is not the right route to pursue.
The best methods of replayability are unlockable content and mini-games. Resident Evil 4 executes this well with the Mercenaries mini-game, which is both fun to play and unlocks weapons for the main game. Ratchet and Clank also succeeds in this regard, as there are hosts of skill points and challenges to play that keep the "fun factor" high. We should pay more attention to game length, as God of War could easily been another two hours and no one would've complained; and I have friends who are still upset that Halo 2 was too short. You can get around this a bit by using downloadable content to "finish" or refresh the game (Hurricane Packs) as well, so I expect that trend to be explored more as time passes on.