When you run the migration in the command line, you can see a broad view of how much progress has been made for each Class. Notice the last line is called the "second pass". I'll explain that more later.
Going to example.com/admin/migration_report/ will take you to this page, showing similar information on your migration progress.
The live update button on the bottom tells the page to refresh the report every couple seconds.
You'll notice as you first start importing, that all of your media objects will jump to "Failed", but they aren't necessarily failed if the migration hasn't finished yet. Those media objects are waiting for the "second pass" (mentioned before) when all the other required items are done importing. For example: derivatives or masterfiles.
You can drill down to a class type and see items and some basic migration info.
Clicking on the an item, brings up a detailed view of any datastreams that are attached to the item.
You can look at the datastreams (including any images) below the header under Fedora 3 or Fedora 4.