Scala is one of those great languages with that one Achilles heel. The speed of that compiler:

   $ time scalac Hello.scala

   real    0m2,907s
   user    0m7,901s
   sys     0m0,308s

   $ cat Hello.scala 
   object Hello{
     def main(args: Array[String]){
         println("hello world")
     }
   }

Implicit type conversion can be debated I guess, but otherwise a very beautiful language.