I've been using the beta version recently, and I think that one biggest omissions are keyboard shortcuts.
Few shortcuts that I'd found most useful:
- focus on search field ("/" or "?")
- go to folder ("g" - brings dialog that allows to type in and jump to folder via fuzzy matching)
- search for tag ("t" - opens up a dialog for typing in tag name, w/ fuzzy matching as well)
- move to folder("m")
Similar patterns could be found in most of email apps, so I guess that these should sound familiar