A great blog entry explains why emacs is so incredibly cool.
Imagine an operating system where you can switch from writing code to browsing the web or chatting without leaving a consistent environment, with the same set of commands and shortcuts. Imagine a set of integrated applications where data is seamlessly shared, where any single functionality can be tweaked, extended and adapted to your particular needs. Where everything is easily scriptable. Imagine, in additon, that the environment provides powerful and complete interactive self-documentation facilities with which the user can find out what is available.
Emacs is that operating system — it really is that cool.