Several of them are over-designed. But the biggest issue, IMHO, is that the lack of closures (which is planned to come in the next version) made a proliferation

Several of them are over-designed. But the biggest issue, IMHO, is that the lack of closures (which is planned to come in the next version) made a proliferation of classes that would have been removed. Just pass a closure instead. Lock api's from the concurrency package are full of examples of this. I don't know if this works on clojure, but Jruby and Groovy solved this partially, by making closures convert into such interfaces automatically. This however, does not solve the problem of the multiplication of classes.