If I was to nominate the two things I find most striking about Mastodon they'd be:
1. the ability to edit posts after posting; this (as my followers will know) is a facility that I use a lot (and thanks to my great crew of typo spotters);
2. the norm of civility that we all maintain; of course trolling & slamming is not completely absent, but at least in my timeline & discussions/conversations civility have been the over-riding characteristic of my exchanges.