hope you ready for that debate...
Time to debate!
Plenty of Pokemon games have good towns, mostly earlier games in terms of exploration and feel, but later games had good environmental art.
Gen 1: Lavender with the Pokemon Tower, Fuschia with safari zone, Celadon with the department store and the back entrances into houses.
Gen 2: Goldenrod with its whole underground and radio tower, Olivine with the Lighthouse, Violet with Sprout Tower.
Gen 3: Dewford is a cozy vibe, Fallobar town feels like a real excursion up and through the ash and is quaint. Sootopolis has the whole gimmick of being in a volcano crater and having to surf from place to place, Mossdeep with the Space Center, Pacifidlog.
Gen 4: Jubilife is a great early town, Floaroma with its cute meadows, Snowpoint with the temple and docks
Gen 5: Hiun/Castlia City -- so many skyscrapers, and the sewer system. Fukiyose/mistralton with the airport, Yamaji/lentmas with the mountains and the haunted manor, the really north one in BW2 with the water gym and beaches.
Gen 6: I remember nothing of these games.
Gen 7: All the names escape me, but I did like the environmental design and some of the flavor text in a lot of the towns, like the early starting town with the coastal road running through it, the resort with the golfers etc. But I think this is where towns started to drop a lot of the integrated dungeon aspects, or distinctive explorable landmarks like lighthouses or even stuff like the football stadium in Gen 5.
Gen 8: Really nice art design but yes, most of these towns didn't have a purspose beyond a gym. Motostoke was probably the standout, as was the ice town in terms of just buildings with unique functions and interiors, but I wouldn't call them particularly great in terms of exploration.