The Pokémon franchise has been using the same basic formula for so long that it has gone from fun to corny to boring to impressive and then all the way back to fun again. The first generation of the series introduced the first 151 monster sprites in 1996 built around gameplay that anyone who's played this year's Pokemon Sword and Shield will find familiar.
You catch Pokémon by fighting them, each Pokémon has up to four moves they can use in turn-based combat, they level up through said combat, and then you use them to catch more pokemon and traverse through the pixelated world this all happens in. Rinse, recycle, repeat, throw in a few hundred new creatures every time, always start with the three cutest of each set for the player to pick from, and always give them the option of giving their rival and battle pets humorous nicknames. But hey, if it ain't broke, don't fix it.
It's not too much of an exaggeration to say that the Pokémon games have single-handedly saved Nintendo's handheld division many times over and the fact that they are still making ostensibly the same game some twenty-five-odd years later speaks volumes as to the staying power of a simple, family-friendly RPG.