To give you a taste of what he talks about, he shows you how much more realistic the water has become in the game. In the older game, the water only flowed in one direction at a constant speed irrespective of where you were. In the new version, water flows at different speeds depending on where you are, and rivers also bend around corners.
That’s just one thing he talks about, there’s a lot of other useful but hard to spot improvements that’s been covered.
Check out the video below to know about them all.