Today's build, according to Microsoft's blog post, includes Start and Continuum improvements that Microsoft demonstrated at its Build and Ignite shows. There's a new tab page for Microsoft Edge that Microsoft also showed off in April at Build, as well as the inclusion of InPrivate browsing mode. Microsoft officials said they believe this build will fix many issues testers have had with the new Edge browser crashing.
That said, today's new Windows 10 Desktop preview build is known to have issues in terms of how well the new Edge ("Project Spartan") browser works on PCs with AMD graphics processors.
At this point, Microsoft is more in the feature refinement and bug fixing stage with Windows 10 Desktop than it is in the adding lots of new features stage. Given Microsoft is believed to be poised to launch Windows 10 Desktop around late July 2015, this is as it should be. (Windows 10 Mobile for phones and small tablets is not going to launch this summer; it will follow later this year, officials have said publicly.)