This thread is shillbait that somehow isn't dead by now but i'll bite.
Character Designs and an absolute bold take: Gameplay.
Everyone can say whatever they want on how the gameplay is just this this and that, but the simplicity of pokemon's battle system that is 25 years old being extremely easy to get into while having its fair share of complexity, although said complexity is NOT as polished for an industry to follow as seen with some strange bugs (e.g.: Defiant doesn't activate if Sticky Web is bounced back by Magic Bounce or Court Change, something that was done in prior games with M.Bounce) but i will give Gamefreak some credit, the battle system has seen improvements over the years by fixing past mistakes and despite powercreep, stuff always feels fresh and even if Dynamax is a complete piece of shit of a gimmick that somehow outdid Mega-Rayquaza in terms of broken mechanics, the other stuff that got less attention was much more polished that you can tell the battle system is not designed by the same team, but i'll digress about the game's development. Stuff like the new moves, new abilities, abilities getting buffed (stuff like Scrappy was given Intimidate immunity), moves getting buffed (Teleport and Multi-Attack being the greater examples) and the new items are far more polished and interesting than Dynamax but unlike Dynamax which is just the cake's dressing, the stuff i listed are all part of the core gameplay.
Put great character designs that appeals to any audience (for the good, the bad and the ugly) and addictive gameplay that despite flaws, keeps getting subtle and good improvements in one spot and that's how you make Pokemon Sword/Shield, a game that has an extreme number of flaws on par with a long list of bugs/lack of polish/outright laziness and you have a game people willingly becomes mentally ill for (from haters to shills)
