>>50226387It has the best stories the franchise has to offer, really amazing soundtracks, and the gameplay is pretty good even if it's babby's first roguelike (which isn't bad - it's a great gateway entry into the genre). The series also arguably makes better use of Pokemon's mechanics better than the mainline series. Abilities, types, even many moves you'd trash ASAP in the main series are valuable in the PMD series.
Also, talking Pokemon is a big fucking deal for many fans. After many years of hearing them say nothing but their names or generic animal sounds (excluding Team Rocket's Meowth, of course), it's mindblowing seeing them say actual words. It makes the Pokemon feel less like animals and more like living, sapient beings.