I'm very, very happy to not be using this language anymore. After my first year on the job, I read some JavaScript code, and I nearly wept at how comparatively beautiful it was.
I found Epic MUMPS to be remarkably readable. Lots and lots of documentation, quite consistent coding standards, and although I would have preferred to write SQL queries rather than MUMPS routines, I didn't find it that abhorrent.
"Some of the contention arose in response to strong M advocacy on the part of one commercial interest, InterSystems, whose chief executive disliked the name MUMPS and felt that it represented a serious marketing obstacle. Thus, favoring M to some extent became identified as alignment with InterSystems."
That's all the convincing I'd ever need. Though having a built-in optionally-persistent B-tree-based store sounds interesting.
SQLite will still perform better though, "heavyweight" SQL syntax notwithstanding.