By far the most incredible thing for me was to see how far a few characters of code can go. Clojure is a very tight language where you can accomplish a lot in just one line of code. You end up suddenly having all this new, extra time to just think about your problem instead of coding it.
Another interesting side-effect of tight code, is that you become a lot less attached to it. When I worked in Java, it would often take 100s of lines of code to solve a simple problem, and once I wrote that code I'd be very hesitant to throw away or refactor it.
With Clojure, it often takes 10 lines or less to solve problems that take 100s of lines of Java. This encourages a lot more experimentation and refactoring in my experience.
Also, since you're always working in the REPL, you can always run the code after you change it and see that it's doing what you want immediately.
