Well... I think Pokémon may not be the best in terms of game mechanics, but it definitely blows its competitors away in terms of monster designs. They are easily recognizable (and thus easily marketable), consistent with one another across generations, and most of all, creative and original. As smooth as games like Digimon, Yokai Watch or Shin Megami Tensei might play, the monster designs get kinda same-y after a while - as they do in direct Pokémon clones like TemTem or NexoMon. I believe that the Pokémon themselves are the main draw of the games, and at the end of the day, that should be the point.
On a side note, this is exactly what makes me dread the recent changes in art direction for PLA and SV. I fear that Pokémon, in an attempt to "shake things up" and regain the favor of a vocal minority of the fanbase, will do away with the particular uniqueness and consistency that defined the monster designs in favor of "polishing" the game mechanics or worse, aping its competitors. Only time will tell, but I don't have a good feeling about the new Mons in SV (with the exception of Fuecoco and possibly Miraidon.)