Fixing that bug where if you do something like upvote someone while typing a comment, your comment gets deleted.
Stop making "Undetermined" the default language for posts and comments, so my feed stops getting spammed by foreign language posts that didn't bother to correctly tag themselves.
Allow blocking entire instances (I think this might be in the latest update which my instance hasn't yet migrated to?).
Beyond that, the only thing I really miss from reddit is being able to open the comment thread for a post and read literally hundreds of comments. Gets a bit underwhelming seeing so many front-page posts with 1 or 2 comments.