Let me define a mini-game for you at the outset. It's when some sort of mechanic or goal in a video game is introduced as a new challenge for a short time which may or may not be instrumental to continuing the progression of the game and has little to do with the majority of the way the game is normally played. You're running around mowing down murder mutants in a first person shooter, then suddenly you have to win a dance contest by mashing buttons to a rhythm. That sort of thing.
There's nothing wrong with mini-games. If Square Enix offered an updated version of the Mount Condor levels from Final Fantasy VII for iOS I probably wouldn't play anything else. That said, sometimes games drop the ball on these little diversions. And sometimes they don't so much drop is as inspire a player to go after the ball with a filet knife until it's a pile of rubbery shreds still warm from the rage of the frustrated.
These are those ball murderers.