This build is the first in a series of builds which will be released, probably with increasing speed, in the build up to the next public release of Windows 10 - the Creator's Update (or Redstone 2 (rs2) release, as it's known internally).
The release notes are available here and show that this build is not about adding new features, but is the first take on polishing the features already in the rs2 builds.
An interesting issue with this build though is that it currently won't install on an x86 based computer; only the x64 version works. Microsoft's answer to this is to simply not release an x86 build at this stage, instead promising an x86 ISO later in the week.
[more to follow]