specific features? how about:
maintaining data integrity - EN constantly overwrites newer files in shared documents. This is a huge problem.
offering proper backups - backups used to be easy a number of years ago. And given the frequent loss of data is critical.
sharing of documents with basic users - Sharing is the #1 reason I have paid for EN premium for as long as I have. No longer can a premium user share an editable document over 20MB with a basic user. It exceeds the maximum note size and can't be editable. This is a recent change for the worse.
lack of a cohesive user interface - sharing a folder/document is inconsistent and different every time they update. In another example, I couldn't find where they had moved the file history feature which I needed due to old files overwriting new files (big sync issues with EN lately). One day its in note info, the next its in a dropdown menu elsewhere ...It changes literally every update and this is very disruptive to my workflow. Also, documentation on the website is so out of date it's to solve these things.
There are lots of other features but these are just a few of the more important core features that EN used to do well but no longer does. The loss of these features makes EN far less collaborative and this adversely affects the workflow. As a paying premium user for over 11 yrs, its sad seeing the decline in quality and usability ....