Shame mercurial didn't catch on. I started learning DVCS' with mercurial, back when they were still a new concept, and git wasn't very good (this is an understatement, git was horrible back then).

What I really liked was the very friendly and usable command line interface, out of the box shortcuts (which I now emulate in my .gitconfig), clear help pages. It was a bit slower than git for enormous projects but it worked wonderfully for me.

Mercurial had a more familiar, but much worse interface than git.

More familiar because it was essentially subversions interface made suitable for a dvcs.

Worse for lacking (or requiring plugins for) features like the index, commit amending, rebasing, lightweight branches, etc.

Git didn't have any of those things either except "lightweight branches". It wasn't until 2006 or so that git grew a reasonable commit command. Before then, people relied on tools such as cogito in order to get work done.

Also, Linux kernel uses git! So it has a traction. Once people get used to a tool they stick to it.