This will focus on the security fixes part. At least what I’ve found so far.
It includes the 4.4.4 security patch that covers the OpenSSL “SSL/TLS man-in-the middle (MITM) vulnerability (CVE-2014-0224)”. Read about about that HERE.
It patches various versions of Masterkey (most/all was patched before this) and FakeID.
So, you’re pretty safe. Just be careful with installing apps that comes from other sources than Google Play Store, since Google scans apps for various things.