It's not just about the REPL and syntax highlighting. You need to see someone use paredit (things like paredit-raise-sexp or paredit-forward-slurp-sexp), evaluate expressions in-place (either seeing the results in the minibuffer or inserting them into the code), use M-. to instantly jump to anything that is defined in the active runtime, etc.
As for debugging, the Clojure experience is pretty bad, compared to (for example) Common Lisp. I'm experienced and use Clojure every day to write large applications, but I still stick to logging for most debug work. And yes, backtraces are horrible.