What's the perfect length of any given game?

[Shinlock]

Shooters - 15- 18 hours
Action/Adventure - 20-30 hours
RTS - 10-14 hours (any longer and I go nuts)
RPG - 40-50 hours min for main quest. Post game 200-300+ hours. I don't mind rpgs taking over 100 hours to finish the core game.
MMO - 8-14 days (played time) to hit the game's level cap.