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