I have to admit Earthbound loses steam at some point but fucking Magicant and stuff like that
It's when you get to Fourside and suddenly the pure linear momentum of the first three towns is replaced by this huge city you're wandering around lost in for hours. You have to go back to the desert. You might have to make multiple trips between the city and desert. Figuring out what to do at this point can take ages if you're not looking at a FAQ.
If memory serves, the game really starts throwing battles at you that are tough enough that you'll have to stop n' grind around that time.
It's no excuse though, you have to play the game because it's fucking brilliant and you need its context for Mother 3, which is fucking brilliant.