The thing I love of git is that its internal structure is very simple and transparent, so for any given repository it is possible (although not necessarily easy, if things are well messed-up) to understand what is going on. It is true that the interface is often messy and inconsistent, sometimes annoyingly so, but if I can understand what things are, I can somehow work out how to do things with them (in extremal situations, I know I can fast-export everything, process with custom Python scripts, rather easy to write, and fast-import again). While if I do not understand what things are, the most powerful and user-friendly tool will have very little value to me. Also, knowing what is git under the hood makes me very confident that I will not lose pieces: as soon as the hash of my interesting commits is in another repository (which is not corrupted), I can do whatever I want with the first one and everything I care will be safe anyway.
All of this depends on me knowing what happens inside git and the git insides being rather simple (a hash tree with a handful of object types); I think I would like Mercurial (or any other DVCS) much more if I knew the same about it: can someone suggest places where this is described?
As a long time mercurial user being forced to switch to git I find that I know more about git internals than mercurial. Mercurial provides a nice abstraction so I don't have to care. In face I've seen a few hints that mercurial has actually changed their internals over the years, but since everything still "just works" I don't think about it. By contrast git is forcing me to care even though I have better things to do with my time.
Sadly github and CI systems provide community tools around git not mercurial (mercurial is an afterthought at best in most CI systems). Those community tools are compelling enough that I'm switching to an inferior system just to get them.
All of this depends on me knowing what happens inside git and the git insides being rather simple (a hash tree with a handful of object types); I think I would like Mercurial (or any other DVCS) much more if I knew the same about it: can someone suggest places where this is described?