Leon Welicki, PM on the Workflow team, has written a great MSDN Magazine article covering the new WF features in .NET 4.5, including:

  1. Workflow Designer enhancements
  2. C# expressions
  3. Contract-first authoring of WCF Workflow Services
  4. Workflow versioning
  5. Dynamic update
  6. Partial trust
  7. Performance enhancements

Leave us a comment with your feedback.  We'd also love to hear about your ideas and priorities for the next release, so please visit our UserVoice site.