People keep ignoring what the definition of fun is, and it makes me cringe and cry.
Fun = The brain rewarding us with dopamine for learning a new skill or getting better at an old one.
Fun is inherit to the game experience. A game is about learning new skills and getting better at them until you succeed in a challenge.
Fun has NOTHING to do with something being happy, something being pointless or something made only for entertainment.
Fun is also personal. Everybody learns differently, and everybody will find fun in different forms.