The url which is currently used as the default
http://www.google.com/search?btnI=I%27m%20Feeling%20Lucky&q=allinurl:, which now takes you to a redirect notice page that requires clicking through a link to get to the google result. I believe this defeats the purpose of the feeling-lucky-url.
I believe the original behavior was taking you directly to the first result. For an example of the current behavior, click here: https://www.google.com/search?btnI=I%27m%20Feeling%20Lucky&q=allinurl:clojure
There is some discussion on this here: https://support.google.com/websearch/thread/15794018?hl=en
Duckduckgo happens to have a query url that works correctly: