Difficulty settings
Another aspect to mention regarding game balancing and tuning concerns the difficulty settings of your game. Most games offer the opportunity to choose the degree of difficulty at which to play the game. This is a key element of any game because it has to do with the degree of gratification that your players will get from playing, and hopefully beating, your game. As personal satisfaction is a highly subjective matter, it can be pretty hard to decide which settings better fit the needs of a specific player.
It is also very important to consider that different game genres and platforms target different audiences. First Person Shooters mainly target hardcore gamers, who expect to be highly challenged by games. On the other hand, the average mobile audience is usually a casual one, so they expect the game to be pretty forgiving and rarely punishing at all.
While setting the difficulty curve of a game, always keep in mind the audience you are targeting and the time you want...