There must be no hints, overlays, suggestions, or predictive insertion of characters as I type. Enabling these distracting features by default is not a fatal flaw, but if I have to spend more than a few minutes figuring out how to disable them, the editor is not likely to get a second chance.
Click a method to go directly to the definition, themes, debugger.
It must be well-documented, extensible, and have good support for Lisp. IOW, Emacs.