Ahh..META II . This is awesome. Was just mentioned again in the "Joe Armstrong interviewing Alan Kay" talk . One of Alan's favourite papers. Joe: "Dan said if you look at this, you will lose a month of your life. And I did" Or words to that effect.
Also the basis for OMeta. I have to admit I've been avoiding it so far in order not to get diverted from architectural insights but this may just be accessible enough to dive on in.