I've used git and mercurial extensively, but only with git have we regularly had the need to summon The Expert. With git I have to tell new users "don't use a flag or setting if you think you know what it does, look it up". That has not been needed for mercurial.

One particular good feature is the concept of a commit phase. It makes is crystal clear when rewriting history is allowed, and more importantly, when it isn't.