Google released a new revision history interface in Google documents. To see it, go to File > See revision history. In 'revision history interface,' you can see what changes were made at a glance. Click 'time stamp' in the right column to see changes made at a given time or use arrow keys to scan through revisions. Changes are color-coded based on each collaborator, making it easy to tell what has been added or deleted.
In the screenshot, deleted and added text are highlighted in orange, while removed paragraph and added comment in green.
Time stamps are also improved in new interface. Now even old revisions are listening: you can now tell afternoon edits apart from all-nighters. The interface also batches revisions into groups of changes to make it easier to understand how a document has changed over time. To see a finer-grained list of revisions, click Show more detailed revisions.