[dkarl]

If you're writing modern Javascript, you're halfway to Lisp nirvana already. Lisp was a huge mind-expander for people like me coming from BASIC, Pascal, and C++. Building programs out of functions was an entirely new way of thinking: writing functions that returned functions, creating abstractions that were parameterized by functions, etc. That is already normal to you.

The other big Lisp nirvana thing is macros, and let's face it, they're cool, but the best way to use macros is sparingly, especially when you're working with other people, so they don't make as fundamental a difference to the way you code as you would expect. At least in my experience; YMMV.

If you're coming from modern Javascript and looking for a big idea that will change how you go about the job of programming, I think working with a static type system will be a bigger eye-opener.