Having never used such a language, I'm curious, what's the debugging experience like? Can I source level step the application in the original language or do I have to debug the generated C?
You can put in line pragmas for e.g. gcc that will point you from "foo.gen.c" to "foo.fancylang". However it is not very useful unless the fancy language matches C's structs and native types and also does not mangle names.