In order to be an IDE, it needs to integrate enough things that are not just editing. How much and what depends on the user a bit.

• For me, I would call anything that only requires interaction with the source files (and some editor config files) to be pure (if fancy and smart) Editor territory. Syntax highlighting, code folding, autocomplete, and even a bit of analysis like "jump to definition". The latter requires knowledge of the language rolled into either the executable or some fancy config files.
• I would consider something that includes buttons for a few external things like diff and docs and cvs to be technically an IDE given the Integration and use for Dev purposes, but dismiss it as an editor with bloat and probably overspecialization too.
• Once the editor hooks into a debugger, then I'm happy calling it an IDE. Breakpoints and variable inspection are a given, being able to eval arbitrary code while waiting at a breakpoint is bonus.
• A "good" IDE to me, would depend on how well put together it is. Stability and UI primarily. This also depends on what competition is out there, as the subjective properties are very relativistic. The number of extra integrations required would also depend on the competition.