New Outlook updates enable you to customize your experience and help you stay focused and organized

Chuck Hildebrandt, sorry for the long delay. I had not seen your comment before. You may have long since figured this out, but to get the full Ribbon Bar back, just click the little drop down caret  in the lower right corner of the ribbon. That toggles between full and compact Ribbon. Changing in any one window will now change all windows (it used to only change it for that one window and instead toggle between showing and hiding the Ribbon). 

Unfortunately, Microsoft has now pushed this fully live for me too. My original problems are still there:

1. No longer possible to have full Ribbon on some windows and collapsed Ribbon on others. 

2. The Header (From, To, CC, BCC) section is still enormous compared to the prior UI (may not be so bad for people who don't use From or BCC -- I can disable BCC, but I can't get rid of the From, because I have multiple accounts, which I need to use regularly). For meetings, where it adds start and end times, it takes up almost the whole window. I can't find any way to make this more compact. 

3. No longer any way to hide the Ribbon altogether. Ironically, this more "compact" Ribbon actually takes up MORE screen space, because I can't hide it like I could hide the old Ribbon bar.

For me, all 3 of those are significant UI downgrades, but I'd also admit none of them really affect functionality. The worst part is that on my smallest monitor, I keep the calendar at full screen all the time on Week view (each day gets its own column). Because I can't shrink that Ribbon without also going to the "Compact" Ribbon on all Outlook windows (and even if I do that, because it's no longer possible to fully hide it, it still takes up more screen real estate in the Calendar window), I can no longer see my whole workday vertically in Outlook Calendar. That genuinely hurts my ability to use Outlook and be productive through the day. 

Frustrating that I reported all of these things during the trial period and Microsoft proceeded to force this destructive UI change on us with no apparent option to revert or otherwise address the very real problems it causes.