Depends on the game. Some games feel too long even though they can be completed in under 10 hours, some games feel short even when it takes 30+ hours.
Other times I don't notice how long it takes but it doesn't detract from my enjoyment of the game... Mirror's Edge I think I beat first time in under 7 hours, but it seemed about right to me and it is a game I like to play through multiple times.







