Sun and Moon have the capability to connect to Bank and transfer Pokemon from Red, Blue and Yellow.
The Pokemon in Red, Blue and Yellow can have moves that they can't in later generations.
The Pokemon in later games have abilities which aren't in Red, Blue and Yellow, as abilities hadn't been invented yet.
With this in mind, which move/ability combos are you most looking forward to that you couldn't access before?
I don't know all the possible move/ability combos, so I can't say I'm looking forward to anything in paticular at the moment.