In all honesty, not a lot. There's a bunch of bug fixes for relatively minor issues (in that they didn't actually break Windows) and there's a big update for enterprise customers relating to deploying Windows 10 in the enterprise.

In essence, the updates now allow system admins to run custom scripts pre and post an install or feature update, meaning more can be scripted and automated, making the number of manual tasks needed to deploy Windows 10 less onerous.

Full release notes can be found here.