It's more than just Evil mode (vi emulation). They have a pretty thoughtful way to organize libraries (layers) and a decent solution to the "how to I manage my Emacs config" problem.
This +1000. Flymake or Flycheck, Autocomplete or Company ? I was in the classic .emacs bankruptcy situation and even started using atom before cloning the Spacemacs repo in my .emacs.d
For those who do not want to understand the details (which in case of Emacs is silly - one miss so many aha moments) bbatsov's prelude is a piece of true craftsmanship.
Pretty simple and doesn't rely on heresy such as evil mode.
Calling evil mode heresy is the same as saying "I wish fewer people used Emacs." Why continue the holy war? You've won many vimmers over... why marginalize us?
I think the creators of evil mode are well aware that it is heresy. They even named it evil mode.
I think the whole holiness of Emacs and the evilness of vim is more tongue-in-cheek than anything.
That's a pretty lightweight Emacs config. Mine is based on emacs-starter-kit (technomancy's creation) and is much larger - https://github.com/metaperl/emacs
Actually, Spacemacs layer configuration uses the use-package add-on ( https://github.com/jwiegley/use-package ) , which helps greatly simplifies and organizes large .emacs config files (and also greatly improves emacs' startup time). use-package was written by John Wiegley, created of the Ledger CLI accounting software, and current maintainer of Emacs. Emacs integration of packages with Melpa gets only a small part of the way towards where Wiegley goes with use-package. . . .
The overengineered/complicated Layers system is why I abandoned spacemacs after trying it. Just installing Evil mode served my needs better.