When the Definitive Edition of Divinity: Original Sin 2 comes out, it will be packed with thousands of "changes that take into account all the feedback...received and will be completely free to everyone" who already owns a copy of the game!
The most significant changes come in an overall rebalancing of the game, a big rewrite and content addition to Act IV and the finale and some re-recording of dialog. There's even a brand spankin' new kraken fight as well.
Check out the video dev diary to see what else you can expect in the Divinity: Original Sin 2 Definitive Edition when it comes out in August!