Mercurial has all the features of a good distributed revision control system. Not only is it incredibly useful as a collaboration tool, I find the ability to track changes and rollback to a specific revision invaluable for working by myself too. Mercurial lets you easily see, down to each line of code, when it was first introduced and why, and tools like hg bisect make tracking down bugs much faster. There are many good graphical frontends such as TortoiseHg and SourceTree that make using Mercurial easier, as well as integration with most popular IDEs such as Visual Studio, Eclipse and IntelliJ.
- Easy to use
- Works as it should :D
- Widely supported (Although not as much as git)
- Good Desktop UIs available (TortoiseHg, etc)
- Good Web UIs available (Bitbucket, etc)
I liked it's ease of use best. If you often find yourself wondering about how to do things with git, mercurial is for you. It offers much less functionality - and that is a good thing.