Art Spiegelman's Maus is one of the most unique and profound works on the topic of Holocaust. Much of that can be contributed to the fact that it's a graphic novel, a term that barely existed when Maus was first published. At the time, all comic book forms of literature were looked down on: from simple cartoon strips in the newspaper to longer, much more significant works. Historically speaking, Maus can certainly be called one of the main reasons critics today won't dismiss comic books as subjects worth of literary research based on their medium alone.
The reasons why Spiegelman chose to make Maus a comic book are various and many. One is that he is an artist; it's his natural way of storytelling. However, almost nothing in Maus is accidental and everything from style to depictions of nationalities as animals serves the story. For example, the Nazis referred to the Jews as "vermin" in their propaganda —a fact of which author was most certainly aware. In the novel, Jews are drawn as mice; although, they don disguises sometimes or change when their self-identification does. This is also intentional, intended to show how crucially important belonging was at the time. For example, a Jew living in Germany today would likely have no problem calling themselves a German. Back then, the lines of nationalities ran sharper. Everyone was painfully aware of who they were and what their place in the world was according to it. After all, the millions of Jews killed during the Holocaust had no other reason of "guilt" than being born.
Now, this issue of identification wouldn't work so well in a non-visual format. All the attempts to blend in would have to be spelled out and explained, while in a comic book, they can just be shown. Art Spiegelman's genius lies in recognizing that; although, of course, his choice of making different nationalities be represented by an animal has drawn accusations of promoting racism. In truth, it's another carefully considered method of storytelling. When you read the book, it's hard to distinguish between people of the same nationality—in mass scenes, you couldn't pick out the protagonist Vladek from the line-up of mice. This is done to enforce the idea of anonymity and the ruthlessness of the Nazi regime. Any one of those mice could be Vladek; in a way they are. We as readers get to hear the tale of Art Spiegelman's father, but there were thousands upon thousands of others who suffered the same cruelty of the camps. The comic book medium allows the reader to experience that lack of distinction in two ways. One, we lose Vladek in the crowd just like the Nazis would have, because from the point of view of the regime, there was no difference between one Jew and another. Sooner or later, they all had to go. Two, Vladek is able to "escape" from our sight because there is no real distinction. The reason for his survival is that he didn't stand out much, didn't raise any trouble, didn't draw attention.
Including the visual side of storytelling, Art Spiegelman is able to say much more with Maus than is written in the speech bubbles. The drawings are one of the most striking things about a book that describes the horrors of Holocaust. The images stay with the reader, as the author has captured something very gruesome and real, all the while drawing cats and mice. The visual is used to give our imagination something to hold on to, emphasizing the darkness of the world it describes, while hiding other things from our sight.