Couchbase Lite Developer Build 003 offers improved database queries, a new query API with two styles - builder and fluent, for development platforms such as Objective C, Swift, and .NET. The new API provides more flexibility and safety features, including subdocument accessors and blob data type support. The release also includes changes to CRUD operations, document change notifications, and thread safety checking. With the introduction of a simplified API, developers can easily interact with Couchbase Lite and take advantage of its features, such as database and document change notifications.