It is not too hard to land on Git for version control nowadays. Although it doesn't have the best user experience or user interface the tooling around git has "won" and there is little reason to look at anything else.
Overall git is fast, has "cheap branches" and the tools and documentation around git make up for what is lost.
As far as RCSs go, Git is no less user friendly than other systems. I've used CVS, RCS, Perforce, SVN, Mercurial, Bitkeeper (the one that caused Git to be born) and others I can't recall. Git is by far the most reliable, fastest, most advanced of any system out there. And if you're not comfortable on the command line, I'd have to wonder what you're doing using Git at all.
And there are always Git GUIs that can take the edge off. Save your time and just get the best one out there, GitKraken: https://www.gitkraken.com/ I use both a GUI when I'm just browsing and the CLI when I'm working.
I am comfortable with the command line and I am strictly speaking of the user experience there. It is partially broken because it exposes quite a bit of the underlying data model. Without understanding that you have to resort to learning certain invocations by heart or looking them up.
One large inconsistency is around `git checkout` being used for multiple actions (not just checking out) - recently this has improved by the addition of `git switch`.
Another big gripe is the inconsistent use of command line arguments and flags, see for instance https://stevelosh.com/blog/2013/04/git-koans/#s4-the-hobgoblin
Mercurial - which you are familiar with - is consistently better than git at everything related to the CLI user interface and experience.
Would you please share few excellent resources based on your experience?