Thanks for reaching out! This type of cumulative reporting is currently being tracked as a feature request for our programmers and I'm happy to add your feedback. (Note: you can always access an overview of your email reporting on the Reporting tab.) In the meantime, you can check the Engagement for a specific contact by clicking on his/her email address and going to the contact details page:
Another option is to export the Did Not Open report to find out who isn't opening your emails. Then you can plan a strategy for re-engaging with them.