So what makes Pokemon fun?
Is it the story? Doubtful. Even though the latest entry in the series, Sun and Moon, had a more character driven narrative than past games, it's hardly the reason people play Pokemon. It's important to remember that in Red and Blue, the first games in the series, there was almost no story. You just had a rival and an evil corporation that kept getting in your way. Gold and Silver picked up the story a tad, but Ruby and Sapphire were the ones that began tasking players with saving the world from some kind of high concept anomaly (which eventually became a staple in the series). But at its core, Pokemon wasn't founded on its storytelling prowess.
Is it the gameplay then? Closer, but probably not. The series has yet to overall its turn based combat, which is starting to show its age. Pokemon battles are still as tedious as ever, where the player hits a single button, and is rewarded with a 3-5 second attack animation that they've seen hundreds of times before. Although it's undoubtedly a series staple, and can definitely have its fun moments, Pokemon GO has made it clear that it's the concept of Pokemon that gets people excited, not necessarily the turn based combat that the series is known for.
Than what is the core ingredient that makes Pokemon fun? Well I'll just say it, because I can't think of a clever segway: It's the world of Pokemon itself. It's the joy of exploring a whole world of monsters and capturing some of your own. It's traveling a region from coast to coast in the hopes of becoming the best in the land. It's going into dark caves and abandoned buildings and dark forests to discovers legends that you can have for yourself! That’s what gets fans excited when they hear a new game is coming out; the chance to explore a new world filled with new monsters.
And Game Freak thinks Pokemon is about the story? Really? By putting story into the game, you’re effectively breaking immersion by forcing the player to interact with characters and go to new locations regardless of their choice. Red and Blue had no story, and to me, it felt like the most genuine Pokemon experience. That’s because no one was constantly telling you where to go or who to talk to. Now in the new games, you’re set on a certain path with minimal chances for genuine discovery.