>>52572899I'd say the more important things that got dropped was the amount of side areas and exploration.
Kanto has stuff like the Power Plant and the Seafoam Islands. Johto has the Whirl Islands and Mt. Mortar. Hoenn has Shoal Cave, the Abandoned Ship, and New Mauville. Sinnoh has the Old Chateau, the Wayward Cave, and Iron Island. And that's just some of the obvious named locations that are out of the way.
Black and White has Mistralton Cave and that's about it, unless you start counting optional routes like Route 18, of which other regions also have quite a few optional paths you can skip over.
BW2 is a bit better with stuff like the Virbank Complex and Strange House providing a couple extra optional locations, but they're not exactly expansive.
Gen 5 didn't drop exploration entirely, but it was the start of a trend of having less and less for the player to go out of their way to check out to offer a diversion from the main gym quest.
