I have interacted much with both Mathematica and Clojure, and the only thing I wish Mathematica had is a coder-oriented editor, like, for example, Cursive in Clojure world. It would become a truly powerful thing. On the quirks of Wolfram language - I personally can live with them, it is good enough considering the requirement to keep Mathematica's historical and huge lib compatibility. However current Mathematica's approach to notebook editing is just a horrible PowerPoint-like mutation.. at least for a coder like myself. I'd even love to help making it better if I had a chance to.