The beta design looks like something I would find associated with Android or Apple iOS. I don't like it. I love the clean, minimalistic designs that I am familiar with in Windows 8.x and 10 and I prefer my Microsoft web apps to reflect that. Being able to choose between the two designs, permanently, might be nice for the users who like more color and symbols. (Actually, the symbols aren't a bad addition.) K.I.S.S.
Thank you for your feedback. We appreciate that you took the time to write to us.
You might enjoy the new Outlook experience more with a few changes to your settings, which you can find by clicking the gear icon. Try changing the setting for Conversation view to Off, changing the setting for Reading pane to Hide, and changing the setting for Attachment preview to Off.
We’re always interested in new ideas, but we need some more specific feedback to fix the problem for you. If you have more detailed suggestions, please update your idea or add a new one.
You might also find this help article useful: aka.ms/outlookcombetahelp. It has some simple steps to fix common problems.
-The Outlook.com Team