For me the complete spec is the killer feature. You can learn Common Lisp in 1990 and write it the same now. As long as we can keep the compilers alive it will be forever.
It’s funny to me that it was critiqued for being “bloated” when now it looks like a focused minimal library.
It's small enough a single person could write a test suite for the whole standard.
Common Lisp wasn't standardised until 1994.
Also, SBCL has some nice features specific to them, I'm sure it's the same for other implementations. So while there's a lot that's common between them all I find myself using a lot of platform specific functions.
Yes, but it existed before then (from 1984 on), and a large amount of code written for CL pre-standardization still runs without alteration or with minimal updates.