For me (used to use vim and moved to emacs) it was the ability to have a full programming language behind me which made me feel like I could truly customise every feature of the editor I wanted.
Incidentally, if you do want to switch you don't have to give up your vim keybindings, there is evil-mode[0] which gives you all the bindings you're used to
[0] https://gitorious.org/evil/pages/Home