What aspect of RPG's has had the biggest effect on you?
That I never stopped daydreaming with friends.
As a child, my constant playmate was my sister, who was only a year younger than me. We would play with either Star Wars action figures (supplemented by action figures from G.I.Joe, Flash Gordon, the Black Hole, and the Fisher Price Adventure People) and spin long yarns playing out stories for hours.
When we got older and started having a pretty stereotypical sibling-rivalry relationship, I still keep dreaming about heroes: superheroes and action heroes and the like. I had discovered RPG's, but really hadn't found the friends with which to play them. I would often just hang out by myself in the back yard, dreaming up stories.
Eventually I found a group, and kept working at finding people with whom I could share my ideas and we could make stories together. Now it's a big way I relate to my children. It's not hard to imagine some parallel universe where I just laid all that aside and just became an adult who didn't dream about heroes anymore but just worked and did what he thought adult people should do. And I'm glad I'm not that guy.