Hello Dan,
Have you tried setting up a filter using the Advanced Filters button? (If not, you need to show the Views and Filters pane on the left, which you can toggle by typing Alt-F1. You can then expand the filter details from the bottom and, in the Advanced group, check "Add Advanced" and click the Setup button).
You could setup a view and add the following advanced filter rules:
IsProject is true AND
CompletedDateTime in the last ? months
You can play with the other filter rules, to decide exactly what you want to show. For example, once you've set up to filter for recently completed projects, you could choose to "Show Hierarchy:Yes" in the General group and then click the button next to the Hierarchy selection to show all the child tasks of the projects. That way you'll have all recently completed projects, with the ability to open the hierarchy and see the status and details of all the tasks under those projects.
Hope that helps.
Stéphane