Depends on the genre. And quality of the game.
Racing - 20+hrs for 80% completion- Only the Forza series manages this.
RPG - 30-50hrs for 100% completion - Something like Mass Effect or Deus Ex is perfect. Witcher or Skyrim are time wasting games for me.
Action/adventure/stealth - 10hrs - Uncharted fit this bill. If its longer, thats great too, like TLOU or Alien Isolation which are around 16hrs for me.
Action/adventure sandbox - 20+hrs - Assassins Creed games and Dying Light can take well over 30hrs for 90% completion.
TPS - 8hrs MAX with addictive online - Halo is perfect for this.
FPS - 8hrs MAX with addictive online - Gears if perfect for this.
Whats unacceptable is sub 6 to 10 hours with ZERO online or ZERO reputability. Order, Vanquish, Bulletstorm, , Fable games etc.
