But I feel like all mainstream programming languages aren't truly "languages", they're mostly dialects of X, where "X" is a fusion of Lisp and C, i.e. same old ideas repackaged in different syntactic packaging.
This is why I am always skeptical about dramatic increases in productivity due to a language switch. Good editor and decent chair produce similar boosts: noticeable? Sometimes. Dramatic? No.
In my opinion two most important characteristics of programming languages are recruiting and maintainability. The former is important because certain languages attract better quality engineers and some are impossible to find experts for. Maintainability speaks for itself: the code should be easy to transform indefinitely, beat into shape, keep improving upon, etc.