As I hopped up on my bloggeyboard and rode the thread wave of recent posts about hexcrawls today, I began thinking of why, initially, I had no idea what they were.
Very early in my experience in the hobby (like, the first time I ever GMed onward) I learned to improvise a great deal. I certainly used modules in the early days but since my players were going to think on the fly to overcome traps and defeat enemies I decided I was going to do the same to challenge them.
The vast majority of my games are about 80-90% ad libbed with the rest being, say, 75% ad libbed. Elements that are not thought up on the spur of the moment (and a good deal of those that are) are based on huge amounts of forethought and research on what would work or be cool in the minds of my players and I and appropriate to the situation they are in. Because of this exhaustive level of pre-game brainstorming, I'm usually ready for anything.
If I have a map of the region and the players decide that they don't want to go to the seek the treasure that they learned about from the ancient Elven runes (the 'adventure' it would seem)...fine. "Where do you want to go?", I'll ask them. If they say north I know that the Celt-like barbarian tribes and faerie creatures lie that way. If they say south I can look forward to whipping up something with the border guard at the edge of the chaotic lands near an old fortress. Go ten miles east, one mile west or just over the water to a group of islands and its the same thing. I know my world and as such I can logically generate what is going to be there where ever they decide to go.
I never thought of hexcrawls as a 'thing' because so many of the games I've run are largely a hexcrawl that leads to something of interest. Even in (or especially in) my Science Fiction games the adventure isn't on Planet A in Building 2, Room X. Its where ever the PCs decide to land and whatever trouble they get into. My worlds and universes are alive and you as a player live in them.
Here's a little story (one of my favorites) from a high school Sci-Fi/Space Opera/Traveller campaign I ran (so we're talking mid-eighties)...
The players were bounty hunters, mercs, smugglers and other neer-do-wells currently shooting it out with their former employers on an industrialized planet. The party performed a task and were double crossed. Now, out maneuvered and outgunned, it looked like the end for our anti-heroes.
Suddenly, one player, my friend Pete, had an idea. Pete was the default team leader and called the group's spaceship on his communicator. He told the pilot to power up the ship and get ready to pick up the rest of the gang. "We're leaving", Pete says. I nod, "You're leaving the planet? Without the money and with these guys labelling you as wanted men?" Pete nods and defiantly says, "Yes! We're obviously not going to get our money and we just won't come back to this system." Now I had no idea Pete would do this...and I couldn't have been happier.
With some quick thinking, wild tactics and teamwork, the players manage to avoid being shot and escape aboard their tricked out freighter. They congratulate each other, high-fiving and laughing about how they essentially 'beat' the adventure. I sat back and smiled. Finally one of them looks at me and says, "So what do we do now?" I looked at him with an inquisitive expression and calmly said, "I don't know. What do you want to do?"
Stunned silence. They left the adventure before it was finished and had no idea what to do next. They began arguing over whose fault it was, what they were supposed to do for money and how they were going to reach another world on the fuel they had. After a bit I stepped in and told them they had enough fuel to reach one of three star systems. One of these system had a gas giant and they could refuel there and then travel further giving them two more destination options.
As they asked questions about the various systems and their worlds and discussed their best course of action, one player said to me, "Hey Adam, what happens if we go here", pointing to a world on the hex grid star map.
"Then you go there and something might happen."
"Well...what if we go here instead", he said in a challenging tone, pointing at a different world.
"Then you go there and something different will happen."
He then looked at the map and then back at me and said, "Wow."