Using Sort, Limit and Expand Folders is a great way create a "what's new" web part.
- Add a web part to the page for the list or library
- From the web part's dropdown menu select "Modify Shared Web Part" and from the properties panel click the "Edit the current view" (just below the "Selected View" dropdown)
- In the Sort section select "Modified" and "descending"
- Expand Folders and select "Show all items without folders" to show all of the documents in the library in a single list
- Expand "Item Limit" and enter the number of items to display
- Optionally select what to do if there are more than that number of items:
- select "Display items in batches" so the users can click next / previous links to page through the data, or
- select "Limit" to display just xx number of items and then display a More link to take the user to the library's page
- Click OK to save the view and click OK to update the web part.