12 hours is a bear minimum (including a second playthough if it's good enough). I prefer my games to be around the 15-20 hr mark, 40hrs minimum for a pure RPG.
If a game has good replay value (more than 3 playthroughs recommended) than 4-5 hours is also fine like the episodes of Half-Life 2. There is always stuff you can miss out first time round.








