MongoDB 3.4 introduces a multi-model database that supports documents, graphs, key-value pairs, and search functionality, designed for mission-critical applications with enhanced security and scalability features. The update includes advanced analytics capabilities, modernized tooling such as MongoDB Compass for visualization, and automated management through Ops Manager for improved operational efficiency. New features like faceted navigation, graph processing, and an updated aggregation framework are aimed at streamlining data handling and enhancing user experience.