Flow describes what it takes for LoL to be enjoyable to a player.
I am gonna just quote from my book, cause I immediately thought about LoL when I read it. Everyone should find it interesting, and Riot developers should find it educational.
Like some concepts of leisure or play, flow is activity which is an end in itself. It is self-contained (autoelic). Psychologist Mihalyi Csikszentmihalyi describes the flow experience as follows:
...a sense that one's skills are adequate to cope with the challenges at hand in a goal-directed, rule-bound action system that provides clear cues as to how well one is performing. Concentration is so intense that there is no attention left over to think about anything irrelevant, or to worry about problems. Self-consciousness disappears, and the sense of time becomes distorted.
An activity that produces such experiences is so gratifying that people are willing to do it for its own sake, with little concern for what they will get out of it, even when it is difficult, or dangerous.
In flow experiences, there is a challenge which is in line with the skills of the individual involved. If the challenge is much greater than the skills of the individual, anxiety is produced. If the challenge is much less than the individual's skills, boredom is produced.
P.S. This post is informative only. I am not trying to persuade, merely to inform and enlighten. Hopefully Riot will start guiding their development by flow more than they do now, because challenge is lacking in this game.