Couchbase 4.0 introduces several new features and enhancements, including the N1QL query language for JSON documents, Multidimensional Scaling for independent scaling of services, and a Global Secondary Index for faster data access. It also offers enhanced security with LDAP integration and auditing, geospatial indexes for location-aware applications, and a new database engine called ForestDB. Improvements in Cross Datacenter Replication filtering are included, and the release boasts a codebase with 1.7 times more lines of code and 2.25 times more tests than previous versions, significantly reducing test execution time. Users are encouraged to explore these features through various training sessions and tutorials, while keeping updated with the public release train and seeking assistance via the Couchbase Forums.