Terra forms are cool due to their utility in vgc, but besides that, eh. I mean look at the towns. There is nothing to do in them besides the gym and some shopping. No npc houses. No additional towers/caves/dungeons/etc in between towns. The open world is cool, but it's much more enjoyable in Legends.

I would say to not buy it, but Pokemon games are and will always be dumb fun. But if you just want the game because of the open world, just play TotK or BotW, if you haven't yet.