Mark Kashman(@mkashman) SharePoint Senior Product Manager on the
SharePoint team, focused on SharePoint Online has published an interesting article listing his 11:) top 10 improvements on SharePoint online.

  1. New user interface (UI)
  2. SkyDrive Pro
  3. Yammer
  4. Guest Links
  5. New and improved Public Website
  6. eDiscovery
  7. Site Mailbox
  8. Enterprise search
  9. Cloud app model (CAM)
  10. PowerShell for SPO
  11. And one for good luck: Storage and file upload improvements

You can see the description of these feature/improvement here