The principal improvement of the new Evernote Web for me is not the design, but a new scheme of URLs.
I mean, that I can take the link to notebook (like https://www.evernote.com/client/web#?b=7b5657265-5731-4515-bc5a-aww20b8c7ba15 (link to notebook don't real, it's example of URL- adress, but you can see screenshots of real notebooks below)
and use this link somewhere in another place (for examle in browser bookmarks).
As result, i can create an (infinity) multilevel hierarchical structure of my notebooks (or single notes) - see left side of screenshots - hierarchy of bookmarks in Safari browser.
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For Evernote- developers: besides tags we need ability to edit (rename, create, add to favorites) and take a link to Evernote Stacks too.