Surprise dropped, as far as I know
https://www.youtube.com/watch?v=gU648Rj3wb8
https://www.youtube.com/watch?v=vtBHGbBLJTU
BDSP didn't show anything that wasn't in the original besides -
HMs are now calling wild Pokemon for you - no need to keep a HM slave in the party
You can call out all 6 of your Pokemon in Amity Square and run around with them
Legends Arceus shows a new Pokemon, new characters and customization options