It's extremely private. It doesn't have Google services by default, but makes it easy to install them as unprivileged apps that - apart from giving you more control over what they can do and limiting certain access by default - work mostly exactly the same way as their privileged installs on other versions of Android. It also lets you disable Internet access privileges to any app that you don't want to have phone home.

Beyond that, most of the other advantages will be less visible. They have hardened memory allocators that make various classes of security beaches significantly more difficult. There's a lot less superfluous background services eating resources. All that and more are listed on their website. It's well worth a read.