Microsoft called a halt to releasing new builds of Windows 10 in mid-December for logical reasons. The holidays were upon us and who cared to test beta software? Well, the holidays are over and Microsoft has returned with a vengeance, dropping a new build of Windows 10 so full of updates it's like a whole new OS.
Build 15002 was released to the Fast Ring of Insider builds, meaning it's known to be buggy and unstable. This is an early version of the Creators Update due in April. The list of changes, additions, and improvements is enormous.