So far, there have been a few things revealed:

1. All Classes (and Subclasses) from the 5e Players Handbook will be available at launch.

2. Custom Characters will have voice acting (you pick the voice at character creation).

3. Spells will have a vocal component when casting.

4. You can recruit custom mercenaries if you don't want to use the party members Larian has made.

5. Feats from 5e will be in the final game.

6. You will be able to select a face type, hairdo, facial hair, skin color during character creation.