For me, a lot of the fun was in making the machine do something it wasn't supposed to be able to do. Or something that was a lot better than people expected it

For me, a lot of the fun was in making the machine do something it wasn't supposed to be able to do. Or something that was a lot better than people expected it could anyway. These days we don't have the same innate hardware constraints, but there's still a lot of fun in working against tight constraints of some sort. For writing silly games I've had fun with the pico8 virtual console, which is highly constrained. I also like playing with speeding up algorithms, that often has interesting time and memory trade offs.