I'll admit it probably doesn't matter too much to existing users, but I do want to do whatever is easiest for new users. If one is slightly better than the other for new users I'd consider it a change worth making.
Today we’re introducing a new sidebar and a new notifications menu into Discourse to help you and your community members find and focus on what is most important to you.
The new sidebar lets you customize your navigation so you can get to your favorite parts of your community, and the new notifications menu that lets you more easily decide which of your notifications deserve your attention now and which ones can be dismissed or be saved for later.
I think this description is rather vague, and I didn't find much more information by reading the 20 or so first posts in that discussion thread. On your screenshots, the sidebar looks like a one-column version of the current menu, moved to the left. But from reading some of the discussion on the Discourse thread the side bar seems to be more than that.
Due to that (IMHO) rather little information, I can't really tell if I'd like the sidebar more. From what I know so far, I don't have a strong opinion, but at least I have some experience with the old menu now. So I'm undecided if I should stick with what we have or potentially get something better.
My understanding is that whether the old menu or the sidebar is used, is a global admin-level setting in the sense that I can't personally switch back to the menu if I prefer it. Is this correct?
That actually looks rather nice, but without creating an account I can't tell how the per-user configuration looks like, which would be an important aspect.