Xtend for a while. It's an improvement over Java, without being a big jump like Scala.
I finally got around to playing with it a little. I took one of my Java classes from jSuneido and rewrote it in Xtend. But I got stuck with some weird errors around array access. I did some searching on the web and found that Xtend doesn't support array indexing e.g. array[i]. I was surprised. You can pass arrays and do for loops over them, but not index them.
I imagine part of the reason for this is that square brackets are used for closures, although in different contexts, so it seems like you could still parse it ok.
Then I saw you can write array.get(i) - more verbose, but more consistent with other containers. (Personally, I'd rather be able to use x[i] or x(i) like Scala for all the containers.)
Then I discovered that the way it handles .get(i) is to wrap the array in another class. This is similar to how Scala does implicit conversions to add methods to existing classes. There's nothing wrong with this approach, but it means allocating a new object for every array access. Considering arrays are usually used for low level efficiency, this doesn't seem ideal. Granted, in some cases the JIT compiler may be able to eliminate the allocation, and if this technique gets common, it's more likely it will be a target for optimization.
It seems like a better approach would be to recognize array.get(i) and compile it to array access byte codes, without any wrapping. Maybe that's hard to do in their compiler.
Another alternative is to leave array code in Java. Which is fine, but doesn't leave a good first impression.
One of the justifications given for not supporting array indexing is that you should use the higher level containers instead. I think there are times when the extra efficiency of bare arrays is justified, but for the most part I agree. And, in fact, the class that I converted could just as easily use ArrayList's rather than arrays, with likely not too much performance penalty.
Even after I fixed this I still had some weird errors left. It turned out that Xtend doesn't have increment and decrement operators (++ and --) Fair enough, Scala doesn't have them either. But I was more surprised to find that it didn't handle += either, although it is listed as an operator in the documentation. For a language that claims "Less Noise", it seems odd to have to write "i = i + 1" instead of "i++".
Once I got past these issues, I was pretty happy with the results. Even without using any of Xtend's more powerful features (like closures and extension methods) the code was cleaner and less verbose, although not radically so.
One of Xtends claims is "top notch" Eclipse IDE support. Unfortunately, that doesn't mean much in the way of refactoring.
I'm still left with doubts about the future of Xtend. It doesn't have the momentum or backing of Scala. With a "smaller" project like this, it could easily stagnate, mutate, or die.