http://www.Gamasutra.com have posted a postmortem of the game, Jak and
Daxter:
http://www.gamasutra.com/features/20020710/white_01.htm
The author raises several interesting points on using a custom language to
develop most of the game code. Their language, GOAL, is based on Lisp.
I think all of the bad points the author raises are applicable to any custom
language.
Some quotes from the article include:
"A single programmer (who could easily be one of the top ten Lisp
programmers in the world) wrote GOAL. While he called his Lisp techniques
and programming practices "revolutionary," others referred to them as 'code
encryption'"
"As new code was compiled, older code (and other memory used by the
compiler) was orphaned, eventually causing the PC to run low on free
memory."
-Luke