Ramin Schokrizade at Gamasutra dissects the techniques money-centered games use to extract the most from their
players victims. One of the games he specifically mentions several times is Candy Crush.
My wife likes puzzle-type games and downloaded Candy Crush because of generally positive reviews. I tried it out too to see what it was like. A few minutes into playing Candy Crush, I realized that the whole reason the game exists is to try to tempt you into buying something. Skill had very little to do with winning. Instead, the power-ups (some of which you can win by playing) were essential for making any progress. I assume that later on you have to spend money to keep those power-ups. I deleted it after a few runs.
In addition to the techniques outlined by Schokrizade in the article, I noted that there is a cool-down timer which eventually disallows you from playing at all if you don't spend money. This is nonsensical if you are trying to make a fun, addictive game; you would want people to play more. This is completely understandable if you're designing something that is primarily a money-extraction machine disguised as a game.
(Via Daring Fireball)