I'll be darned. Whole time I've seen it in VMS-related material I thought it was just a pre-processor for ASM or something. Turns out it was a sort if C competitor. Thanks for the tip. :)
No problem. I'm trying to remember when I first learned about it. I want to say it was a compilers (?) course in grad school. The professor was lamenting that C had survived and BLISS had disappeared, led me to research it originally. I particularly like that everything (or nearly everything) is an expression, probably due to my affinity for functional programming languages. Beyond that, I'm not sure that I like it's typeless nature for doing systems programming work. I guess it depends on how low-level you're talking about, though.
EDIT: I recall reading more about BLISS back then, but that was a decade ago. This [0], linked in the Wikipedia article, is pretty interesting. I'm about 5 pages in and have to head out so I'll finish it later, but it seems like something you'd be interested in given your general interest in language history (from reading your posts in the past).
It included a macro facility, but it was also a full-blown systems programming language.