Besides that you are REALLY active while playing a game in contrary to just stuff the couch and watching a movie, just show him these episodes of Extra Credits:
(not final)
http://www.escapistmagazine.com/videos/view/extra-credits/3261-The-Myth-of-the-Gun
http://www.escapistmagazine.com/videos/view/extra-credits/3167-Gamifying-Education
http://www.escapistmagazine.com/videos/view/extra-credits/2957-Tangential-Learning
http://www.escapistmagazine.com/videos/view/extra-credits/3080-Games-You-Might-Not-Have-Tried-or-Heard-Of
http://www.escapistmagazine.com/videos/view/extra-credits/2633-Non-Combat-Gaming
http://www.escapistmagazine.com/videos/view/extra-credits/2414-Facing-Controversy
http://www.escapistmagazine.com/videos/view/extra-credits/2264-Symbolism-101
http://www.escapistmagazine.com/videos/view/extra-credits/2545-Narrative-Mechanics
http://www.escapistmagazine.com/videos/view/extra-credits/2175-Diversity
or better YOU watch it and build your arguments from there.
good luck

a good presentation also will show YOUR FATHER how much YOU care about games
and that you are not the blind degenerated Zombie that he thinks you are when you are gaming.
And don´t mention GTA - EVER!
EDIT:
Also build on analogies he is familiar with. Books, movies, even sports. If he doesn´t read or likes movies, ... then you will have a really hard time.
Games:
Portal, Incedrible Machine, Blueberry Guarden, Braid, The Path, Samorost, Machinarium, Amnesia: The Dark Descent, Ceville, Monkey Island, Sam & Max, Syberia, Longest Journey, Osmos, Crayon Physics, Civilization,