- You can use whatever paradigm you want.
- Most implementations are fast enough.
- A competent programmer with expert guidance can be effective in common lisp within a day.
- It has many functions, perhaps more than any other language
- It is tricky to implement fully and correctly (I used to contribute to ECL; Embeddable Common-Lisp)
Lisp is perhaps the most effective language.
ESR says: [LISP is worth learning for] the profound enlightenment experience you will have when you finally get it. That experience will make you a better programmer for the rest of your days, even if you never actually use LISP itself a lot. (You can get some beginning experience with LISP fairly easily by writing and modifying editing modes for the Emacs text editor, or Script-Fu plugins for the GIMP.)
However RG says: I just wasn't a very good programmer any more. Lisp's power had made me complacent, and the world had passed me by. Looking back, I actually don't think I was ever a very good programmer. I just happened to have the good fortune to recognize a good thing when I saw it, and used the resulting leverage to build a successful career. But I credit much of my success to the people who designed Common Lisp.