I found the syntax pretty terrible, worse than Java in several ways. In particular, too complex. I also found the object system overly complicated (and I find Haskell's ok).
It's slow enough -- why would you want to make it even slower?
And it compiles to Java source code, which makes it an ideal language for Android development.
It's like the Kentucky Derby. There's the big 4, scala, clojure, JRuby and groovy, all nice languages. Then there's the little 5: kotlin, ceylon, gosu, fantom, Xtend. Gosu and fantom are worth trying, I just haven't got around to it..
But to each their own.