This is my fouth game jam (all gamdev.tv ones) and in the past I have tried something different every time (FPS, platformer, and card game), but this year I have been really pushed for time (I had to submit yesterday as I'm at a festival for the rest of the week). I was still rewardind though as I hadn't got the chance to do any game dev for almost a year, so it was fun to get back into it and see what I could remember. I've been going through a gamdev.tv Blender course most recently, so if I had the time I would have liked to write a game using my own models and animation. Maybe next year :)
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3D modelling can be very time consuming, I have done some simple modelling for my own projects, but not yet completed anything for a jam, I recently tried to make a 3D game for the recent underwater horror jam, but missed the deadline.
If you want to make a 3D jam game, you might have to work on your own assets over time and then use some of them in a jam in future.
I have found that making 3D assets and a game in short time frame is quite difficult if you want to include more than basic shapes or a basic game.
Good luck with the jam