When I used to play in junoir high school, we played hardcore sessions, 12 hours in length or more, battles upon battles, ignored rules, built small fiefdoms that made no political, social, or economic sense, and globetrotted from campaign setting to campaign setting...from the Temple of Elemental Evil in Greyhawk to battling gnome things in Kara-Tur, to taking to SpellJammer to Bral. We liked stories that were simple. There was also few people who played, my group was three, maybe two.
Things got more complex through high school, especially at the end when colleges were looked at, serious girl involvement, and a falling out betwixt my gamer friends and I.
By the time I started college, I had gotten out of gaming (and missed most of 2nd edition D&D entirely).
Five years and a B.A. later, I'm working at a local ISP and meet some folks who are just starting 3rd edition and I began to play again.
Now, 7 years later, here I am, fully immersed in the hobby again. Going to Gencons, playing multiple systems, talking about it as a hobby instead of as a cool thing to do on Saturday.
I think 17 years has given a breadth of experience that has fed into my gaming...
I don't want black and white stories. I want much gray. In the games I run, no matter what system, there's rarely a happy ending. There's doubt and questions unanswered...black humor, flawed good guys, redeemable bad guys, and people who are just in it to win it. I couldn't imagine playing games like Toon, where faniciful silliness reigns. Dark, disturbed, provocative, slightly realistic are how I like my stories.
I ran a D20 Modern game months ago that's on hiatus. The PCs beat the killers, rescued some people, uncovered a buried secret that brought the truth to bear.
But the PCs didn't feel victorious: they looked at what they lost...as much as they had gained. Men and women corrupted or dead, careers in flames, family members lying in the hospital dying, one PC dead, another emotionally and psychologically scarred, and a mother forever plagued by the hideous murder of her child.
Yeah, that's how I like my stories.
But form wise, I tend to run campaigns like Joss Whedon TV shows. A campaign arc (tv season) of connected adventures (episodes), culminating in big event (season finale). The beginning of the next arc has to finish up the big event and/or deals with the fallout from the previous arc's events.
Flavor-wise, my campaigns tend to be more like 6th-7th season Buffy the Vampire Slayer....a bit hopeless, bleak, characters at odds with the world around them, etc.
I'll say more age breeds more complexity and more grittiness, more character and less in your face POW.