This is my first game jam in a long while, and it is also the shortest one I participated in- I had three days to create a game. In this jam, the themes would be randomly generated and announced 24 hours prior to the jam. I wasn't sure I would participate if I couldn't think of a game idea in one day, but this window of time was apparently enough to create a game around the 'Defiance' theme.
Back in the Flappy Jam, I battled it out against my brother. We both delivered a game, and he won (because he had received two ratings, and I one). This time we tried battled it out again. My brother, not as skilled as I am, came short in time and only created a puzzle game featuring a dog that shoots lasers. He is still working on the game, though, so we'll see what he makes of it.
First, I started out creating more of a sandbox. It was a city. I made it somewhat lively by placing lots of different objects, creating them as I went, rather than thinking of a gameplay objective for them first. This is rather interesting- instead of creating a goal for the game first, I created the means, the toys to reach an eventual goal. It was, and maybe still is, more of a playground than a real game. This isn't a good or a bad thing, it's just something that I've never tried to achieve in a game before. It is very interesting game design by itself.