I'm a big fan of prototyping, that period in a game's development that's fast, sometimes dirty, but mostly exploratory. Trying to find answers to myriad questions: Will this idea work? How will this idea work? Is it fun? Is it interesting? Is it different? I find prototyping, especially rapid prototyping, a challenge, but a rewarding one.
I have several prototypes on my itch.io page as well as on my Patreon. Sometimes, when I'm feeling burnt out on a project, I'll take a few days, or even hours, just to prototype something sloppy, get an idea down and see if it inspires anything elsewhere or just put it in the "fridge" never to see it again.