It seems to me that as one advances in the game the balance between a player’s skill and the algorithm becomes, well, unbalanced. I don’t consider myself an “expert” player—persistent might be a better description, and it seems to me that even some so-called easy levels require a combination of boosters and additional moves in order to complete. That takes a lot of fun out of the game. I enjoy challenging myself, but when one has skillfully combined special candies—multiple times—on a level and suddenly the moves dry up, it just isn’t fun. If it happens once or twice, so be it, But when it happens over multiple times over multiple days, it just isn’t fun.
There was an article in the Wall Street Journal several years ago (April 7, 2015) about the design of the game. As I recall it said that a “hard” level might require as many as 50 attempts and an easy level 3-5. I’m good with that, but it seems that isn’t the standard anymore.