Good question
I think that Norvig's PAIP code is generally good (although IMO it's nicer when rewritten to Scheme), but I find CLOS-heavy code more difficult to digest.
I find that Common Lisp in general has some 'ancient' vibe, which I don't necessarily like. I much prefer Scheme's recursive functions, named let and map/filter/append-map to CL's loop macro, dolist etc.
(Scheme also has the CL-like "do" syntax that I don't understand, and don't want to understand)
There are some things though that are tragic in Scheme (like records and modules) thar are at least acceptable in Common Lisp.