1) Uses Chrome's font renderer - it looks terrible on Windows
2) Indent = Tab size
3) Themes can't properly customize some key on-screen assets
4) No macro recording/playback
5) Can't edit enormous files
Other than that the add-on ecosystem can be a bit fiddly, and you won't find syntax highlighting for more oddball things that you'd 100% find for vim or Emacs.
Oh, and sometimes it ends up using 100% of the CPU in the V8 GC. Might be add-on related.