The new major features are certainly
- support for Java NIO (using the Netty framework), which is a corner stone for future development (like an XMPP server or Serverless Messaging),
- improvements to the JID implementation (e.g. it now uses the upgraded PRECIS framework as per RFC 8264)
- and support for XEP-0390: Entity Capabilities 2.0 and XEP-0392: Consistent Color Generation.
Further information about the release can be found in the release notes and in the changelog.