The first public preview of Office 2016 and therefore also Outlook 2016 has been released.
Office 2016 Preview can be downloaded here:
https://products.office.com/en-us/office-2016-preview
Reason enough to take a first look at the upcoming Outlook 2016
When Outlook 2016 is started for the first time, not much has changed visually; the account is set up first
After setting up the account, I think Outlook is a little tidier than its predecessor:
Very reminiscent of Outlook Web App 2013 
Apart from the design, I haven't noticed any major changes so far
I find the feedback function quite nice, even if it is probably no longer to be found in the final version.
I'm going to play around a bit. You'll find the highlights here.