Windows 10 Mobile build 10166 was released to Windows Insiders earlier today and as per usual we've taken our hands and placed them all over the new bits. Build 10166 is pretty similar to 10149, so there's not a lot new to detail.
A couple of new additions in this build are the Edge and Store tiles being transparent, the app open animation has been sped up and is a little smoother, and overall build quality feels excellent.
If you're a Windows Insider waiting for a good build to update to, I believe 10166 is a good build to start with. Make sure you check for updates via Windows Update once registering with the Windows Insider app to get updated!