I feel the same. I used to be able to get uncountable hours of gameplay out of simple demo's of games because I didn't have the money for full games. The examples that come to mind are Cavewars and Fallen Haven. Both strategy games with a time limit. My brother and I would play the demo level over and over again and try to progress further and further within the set time limit. In a way it was like speedrunning but the other way around.