How does it compare with powerful IDEs like Intellij/PyCharm or Eclipse? I mean, does it make sense to have an editor that is both good at "code, html and prose" (debugging and refactoring comes to mind...)?
ST makes navigating the code more quick and smooth - the minimap takes away the feeling of looking at code through tunnel vision, you can preview files much more quickly, and view more code at once with minimalist full-screen mode settings and multi-column layout. The regex search with active highlighting in both the minimap and the file is also nice, and multi-select is pretty helpful for refactoring repetitive code.
That said, ST is just a text editor, not an IDE - while some features, like autocomplete, are partially compensated for, it doesn't do type checking or follow references across files, so other features that stem from those will be missed; e.g. refactoring across multiple files is usually faster in Eclipse. I would usually do most of my editing in ST, and then type-check, compile, and debug in Eclipse.