A couple of years ago, Lisp luminary Nikodemus Siivola rescued and reposted Abhishek Reddy’s Features of Common Lisp page. It serves as a nice introduction to what makes Common Lisp such a great development environment. It doesn’t, of course, cover every feature and it doesn’t examine the ones it does cover in depth. Still, it’s a useful resource for someone who wants to see what the excitement is about.Even if you’re an experienced Lisper, you may find it interesting. It’s well worth a look.
While you’re at it, you might also want to have a look at Siivola’s Common Lisp FAQ. I’ve mentioned that a couple of times before and highly recommend it.