- It requires a running JVM to compile it all down (not a bad thing).
- Can take upwards of a second to compile depending on code base size and compression setting (even if the JVM is warm).
- Kills all ability to debug. Looks like "a.call().call()" etc.
That said, ClojureScript has been fun to work with, but IMO, Google Closure as dependency thwarts a lot of people looking to try it out like they might try CoffeeScript or TypeScript.
http://cljsfiddle.net/ goes a long way towards having a tool people can just play with to try out ClojureScript without being twarted by setting up Clojure/JVM/Lein/Lein-cljsbuild/
Maybe I'm a bit of a masochist, but it's not that hard to read the compiled output, especially when you have a decent mental model of what it should be. It doesn't look like idiomatic javascript, but the structure is pretty regular.