What Makes a Powerful Programming Language?

A not-so Anonymous Coward queries: "My company is about to start development on a new project, and I have to decide on a language and development environment. My boss gave me a set of criteria which needs to be filled: intuitive and easy to use IDE; simplified GUI design and event handling; advanced error handling; advanced object oriented design including multiple inheritance, abstract classes, and garbage collection; full support for operator and function overloading; and portable (at compile-time) across various platforms. I have already looked at C++, Java, C++, C#, Eiffel, and even VB.net; I may be missing something but as far as I can tell all of these languages are missing something from this list. Is there a language available that has all of these features? I thought that someone from Slashdot would be able to point me in the right direction?" If you were to design a language from the ground up, what features would you include and why?