Mmm, I've never used Ruby or Rails professionally, so I can't really speak to that. Prior to Clojure, I mostly worked with C++, Java, C#, and Python.
At its core, Clojure is basically just data and functions. Once the switch flipped in my mind, I found that to be simpler and more straight forward than any of the languages I worked with before.
When the majority of your code is side-effect-free, pure functions (and Clojure makes it very easy to structure your code this way), it becomes very easy to reason about. And very easy to test, with minimal ceremony!
P.S. When I was learning Clojure, I kinda devoured all the resources I could find. A couple interesting looks at the language from the perspective of Rubyists:
http://briancarper.net/blog/536/clojure-from-a-ruby-perspect...
http://confreaks.tv/videos/rubyconf2009-clojure-for-ruby-pro...
