RethinkDB 1.7: hot backup, atomic set/get, 10x insert performance improvement
10x insert performance improvement seems very small considering this simple benchmark someone did:http://stackoverflow.com/questions/15151554/comparing-mongod...  MongoDB: 0m0.618s
  RethinkDB: 2m2.502s

Although as stated in that post, this is likely because of the different fsync() policies between the two databases.