I want a bucket of fixes alongside a big content push.
Give me Monk, Paladin, and Sorcerer to play around with.
Make it so Wizards can't learn EVERY scroll - there's some blanket command they have in there to make things quick that needs to be modified. Wizards shouldn't be able to learn divine spells.
Take surface effects off cantrips, reserve that stuff for stronger spells. Make Firebolt the proper damage and just get rid of the fire surface effect.
Lots of things that have been already said toward making things consistent with 5e rules.
Fix Bless & Bane actually affecting more targets as the spell is cast at a higher level.
More Subclasses! Pepper in a few more, maybe not ALL of them at once, but just some more from the base PHB.