At what point does a game's length becomes an issue?

[HoloDust]

I tend to compare hour/$ value in games with TV shows, which fall into $4/hour (or $3/45min) - this translates into 15 hours for $60 game.

Of course, if it's a great experience and/or if it has good replayability I'm more than willing to bend this self-imposed hour/$ guideline.