I just did BW1's postgame for the first time ever on Monday!
There's not a whole lot to it, especially with wifi gone. If you wanna complete the national dex, a bunch of older gen pokemon are in eastern Unova.
A couple new legendaries to catch, higher leveled E4 with an actual Alder battle, new superboss, finding the remaining six sages for Looker and diving into an ancient castle underwater for Arceus' plates and some treasures.
Can all be done in a few hours, but the levels for trainers jump to the mid 60s immediately so you might need to grind.
She/They, no substitutions~