Screenshots of Windows 10 Mobile Build 10149 have been posted by MSMobile and these reveal many major and minor changes. It also seems that the Build has improved performance and is as fast as official release builds.
One of the most interesting change is that action center now has four rows of quick-action buttons and now includes Torchlight, Data Toggle, Battery Saver and Quick Note action buttons as well.
The volume icons have changed in the quick-volume bar.
Spartan address bar has moved to bottom now. You can now also choose between Mobile and Desktop versions. Hub has new icon.
OS now offers options to open PDF documents.