>>34362188B/W DOES have a ton of areas to explore, just as big as any generation before it, just because the story mode makes you walk in a straight line doesn't mean the actual places you visit are small, Castelia city is HUGE, and plenty of dungeons like chargestone cave are BIG too.
the only difference in B/W compared to past generations is that you can take less detours in the story mode, but like I said, those detours dont make those maps bigger than B/W is, its still one of the largest regions in all of Pokemon, and MUCH huger than kanto for example.