Essentials is a domain controller, and Microsoft HIGHLY recommends that you migrate (eg run two systems, add the new system to the domain, and then decommission the old system).
In place upgrades can BREAK the server and domain.
If no systems are joined to the domain, then a Clean Install is recommended instead.
AKA, Microsoft does not recommend upgrades for servers.
if you're on 2012R2 Essentials, then I'd recommend sticking with it. It works, and there isn't a huge change in features here.
The big change is the underlying OS to the Windows 10/Server 2016 base.
And that's mostly UI changes.
The biggest changes I've seen:
Windows 10 ADK for the client restore stuff.
Windows Defender on the server
Moving the "Safe mode settings" into the dashboard
Can act as a secondary domain controller
Windows 10 base
