Dan Mosely recently posted a feature poll on the MSBuild blog. Here are the results. Debuggability topped the list over more traditional features. I found that very interesting.
My goal is not to comment on how feasible this is or suggest how to accomplish it or even say whether I personally agree. Rather it's just a great example of how valuable a good debugging experience is for a language.
Overall, the CLR has put tremendous effort into debuggability, including major whidbey (2.0) features like Edit-and-Continue and just-my-code.
See also: Measuring language complexity: Do you need a debugger?