I've been playing RPGs for most of my life. I like 'em a lot, that goes without saying. But my tastes have changed over the years.
Maybe yours did, too.
I started in grade school in the 80s, playing the Red Box edition of D&D. I learned it was more fun to play pretend when you didn't argue about who died and who missed.
Then I moved on to Marvel Superheroes and Paranoia. Paranoia taught me that it was okay to make things up outside the module and to "fudge" rolls. Marvel taught me that, even though I'd rather choose who I am in a game, it's sometimes fun to have other people make changes or accept their suggestions.
Then along came Call of Cthulhu... where I learned that it was more fun to just give players the clues they needed so we could all enjoy the mystery.
After that I played West End Games Star Wars, Cyberpunk, Teenagers from Outer Space and Ghostbusters, all of which taught me that it's cool to give players points with which to influence events. They also taught me that my imagination isn't always the most important one in the room.
By then I'd got into college (1989) and played just a whole bunch of stuff. TORG, Nightlife, Ars Magica and, God Help Me, WoD (although we defaulted to Hunter's Hunted stuff.) These games all taught me that style over substance sells (but not forever.) Players like what they like. Also, I learned that people don't cooperate just because the rules say they should. They cooperate in exchange for a reward.
The 90s brought In Nomine, which taught me that interesting dice conventions need to be focused in order to work. I also played Feng Shui, which taught me that what you need to do something ought to be available when you think it ought to be done.
They also brought Castle Falkenstein which taught me that having more control over what happens to your character, or being able to better anticipate the choices you're going to make is a lot of fun and makes you feel more confident. I thought cards were the only way to do that for a long time.
Near the end of that decade I got into Unknown Armies, which taught me that watching my character change emotionally (primarily with its Stress/Rage/Fear/Noble/Obsession) system was satisfying and that people will do insane things for a bonus to their rolls. Oh, and FUDGE. How could I forget FUDGE, which taught me how to divorce system from genre and then recombine them in ways that made more sense.
And about that time I got into story games. I'd heard about them here and there, read some of Lumpley's essays, but PrimeTime Adventures was my first one and I thought, "hey, some of these guys have learned the same things I did... but they took it a step further!"
What kind of learning process made other people think getting on this site was a good idea?