Conceptually speaking, it remains (despite various flaws and warts) one of very, very few well thought out pieces of non-trivial software. For decades, emacs was pretty much the only program with a search function that didn't suck. Emacs is still the only program I know pf with a decent, branching, undo system and proper, non-alzheimered copy-and-paste. Vim has branching undo system, and a clipboard that can hold more than one item, but both work poorly (e.g. in emacs it's ergonomic to cycle through clipboard history or pull a clipboard item by textual content, in vim it really isn't). Emacs is also remains far more deeply extensible and self documenting than anything else I can think of.