I was paging through some old symbolics lisp machine code the other day and while I found some subtle differences in style, it was not so different from modern CL code. I think the differences that are to be found are less about the way one writes lisp and more that these days people make use of "standard" things like quicklisp, alexandria, fiveam, and other utility/portability libraries that didn't exist back then.

Edit:

I suppose a major change was that back then, CLOS was not yet part of the standard. There was a competing system being used at the time called flavors that had a lot of the same features. No one uses that anymore to my knowledge.