[itcmcgrath]

Great question! I'm the PM for both Cloud Datastore and Cloud Firestore.

The biggest difference is the integration with Firebase, so you have access to Mobile (iOS/Android) and Web SDKs along with a native offline mode. This comes along with the real-time synchronization feature that makes serverless app development a breeze.

Cloud Datastore is great for large scale server-side development where you manage your own connection to your app, such as running your own website on App Engine or via Compute/Container Engine.