The ability to have our entire infrastructure managed in one place, including all of my servers (physical or virtual).
It's been great having everything under 1 roof! I wish there was more integration between services like Office 365 so that we could manage both from within the same interface. We've really found it easy for us as IT administrators to be able to access information about users who are not logged into any Microsoft product remotely - whether they're using Windows 10 at home or Mac OS X at work.