See the documentation for the changelog[1] or Jira for the ticket list[2].
As always, please let us know if you have any problems by opening an issue at https://jira.mongodb.org/browse/SCALA.
The JVM Driver team
[1] http://mongodb.github.io/mongo-scala-driver/2.2/changelog/#2-2-0
[2] https://jira.mongodb.org/issues/?jql=project%20%3D%20SCALA%20AND%20fixVersion%20%3D%202.2.0