Over at The Setup they are featuring Phil Hagelberg who has an especially nice take on what makes Emacs so great. He says that Emacs is as close as you can get on modern systems to the fully dynamic environment of the Lisp Machines of the 80's. Almost any part of the environment can be changed at runtime without recompiling or restarting.
I think that's exactly right. There are, I suppose, Emacs users who don't change anything from the default setup but as Irreal readers know, I have all sorts of customizations to my Emacs and I am not in the least unique in this. One of the nice things about this is that I wrote those customizations using the same mechanisms as the authors of Emacs itself. Hagelberg says, “It's hard to overstate the benefits of this setup.” It's something that you get “for free” because when we make extensions to Emacs we're writing in Lisp and as Doug Hoyte says in Let Over Lambda, “…lisp gives you the same tools available to the people who created your programming environment.”
Hagelberg goes on to say that this reduces the friction of tweaking your environment to such a low level that you're more willing to experiment and improve things than you would be in a more standard environment. For example, I use OS X and really love it but it's too hard to make anything other than fairly simple changes to the default behavior and most of those are changes that the system implementors anticipated and provided some way of effecting. I would guess that this ability to customize things is the reason that many Emacs users try to avoid leaving Emacs at all, choosing to read and send mail, use IRC and IM, listen to music, and many other things all from Emacs. Why not? You can pretty much have it anyway you want it.