Dart provides a complete "Batteries included" solution, i.e. Dart IDE, package manager, core libs, etc. Optional typing enables IDE's to maintain richer knowledge about your code, enabling proper intelli-sense and refactoring support. Dart IDE's intelli-sense is smart it can even infer types inside string literals:

http://news.dartlang.org/2012/08/dart-editor-improves-on-cod...

var v = document.query("input#id");

v. //brings up intelli-sense for InputElement

You can also debug natively in Chrome or inside the Dart IDE. JetBrains are also developing their own plugin for Dart: http://plugins.intellij.net/plugin/?idea&id=6351

It also transpiles to JS (like CoffeeScript) but also includes a Dart VM which contains innovative features like Snapshotting for instant start-up times.

The original post was about a "slightly better java", so you're right, I tried to enumerate some features that might be interesting to a Java developer.

I really don't like X vs Y stuff (too many subtle and contextual issues), so I'm just trying to help the original commenter dig a little deeper.