Many huge Java frameworks are painfully over-complex, but personally I make good use of a lot of "tiny" Java libraries. e.g. if I want to calculate an MD5 checksum or pluralize a word, there's usually a bit of Java out there for that already. Joda-Time is a good example of a clean Java library that's fairly painless to use from Clojure.
And then sometimes people have written Clojure wrappers around Java frameworks. Ring/Compojure as a thin layer over Java servlets is a good example. clojure.contrib.sql is a thin wrapper around JDBC, so that Clojure can already talk to a wide variety of databases.
In that case you get the benefit of a solid codebase as well as the benefit of a clean Lispy interface. Not sure how much more you could ask for. It would likely take years to reproduce all of that work in pure Clojure.
And then sometimes people have written Clojure wrappers around Java frameworks. Ring/Compojure as a thin layer over Java servlets is a good example. clojure.contrib.sql is a thin wrapper around JDBC, so that Clojure can already talk to a wide variety of databases.
In that case you get the benefit of a solid codebase as well as the benefit of a clean Lispy interface. Not sure how much more you could ask for. It would likely take years to reproduce all of that work in pure Clojure.