Difference between Google Cloud BigTable and Datastore

The main differences are:

• BigTable seems to be designed for HBase compatibility, whereas Datastore is more geared towards Python/Java/Go web app developers (originally App Engine) 
• BigTable is 'a bit more IaaS' than Datastore in that it's not 'just there' but requires a cluster to be configured.
• BigTable supports only one index - the 'row key' (the entity key in Datastore)
  • This means queries are on the Key, unlike Datastore's indexed properties
• BigTable supports atomicity only on a single row - there are no transactions
• Mutations and deletions appear not to be atomic in BigTable, whereas Datastore provides eventual and strong consistency, depending on the read/query method
• The billing model is very different:
  • Datastore charges for read/write operations, storage and bandwidth
  • BigTable charges for 'nodes', storage and bandwidth