The graphic novel that changed my understanding of what comics can do is Chris Ware's Jimmy Corrigan: The Smartest Kid on Earth. It is not a comfortable book. The protagonist is one of the most comprehensively defeated characters in any medium — lonely, incapable of connection, unable to assert himself in any situation. The book is about the transmission of damage across generations.

What makes it a masterwork is the formal language Ware uses to tell this story. The grid layouts, the color palettes, the scale changes, the juxtaposition of past and present — these are specific choices that have meaning. The form is the content in a way that prose fiction approaches but can't quite achieve.

I recommend it alongside Building Stories, which is Ware's other major work. Together they represent the most formally sophisticated comics I've encountered.