I just spent an entire weekend playing candy box 2 and I had so much fun, I made a donation to the dev. First game I've played to the end in years. There's something about making a number go up (in the game, it is candies) that satisfies my curiosity in a way I didn't think I needed.

I got to use my math skills (estimating when some scheme would make the number reach a certain level. I got to use my research skills (searching the game wiki for schemes to make the number reach a certain level). I got to use my puzzle-solving on some of the minigames. I got to be patient while waiting for schemes to pay off. I got to be persistent when grinding through some minigames to make the number go up. I had something to look forward to whenever I was bored throughout the day.

Thanks to the dev, aniwey, and thanks to the HN poster who started the thread about Universal Paperclips on which I found a reference to Candy Box 2.