Maus is a two-volume comic book memoir written by the son of Auschwitz survivors, about their story of survival and also the author's story of his somewhat difficult relationship with his dad. (An aside here - I had a hard time coming up with that first part, because I didn't want to say "graphic novel" [it's not a novel] and "graphic memoir" sounds like a Penthouse exclusive, and "comic book memoir" sounds kind of dumb, but it's the best I've got. ) As the inside flap of the book says, it's a story about the Holocaust and also a story about those who survived the survivors.
We've all seen/heard/read a million stories about the Holocaust at this point. It's horrible and heart-breaking every time. It never gets easier to witness in any way, largely I think because most people have a very difficult time imagining how anyone could treat another person in that way. People have treated other humans as animals or worse throughout history, and it still goes on today (which is partly why the stories are still so relevant and raw), so I know the attitude is certainly within the human capacity...but I don't understand it. Spiegelman ups the ante a little by depicting the characters as animals already - the Jews are mice, the Nazis are cats, the Poles are pigs, the French are frogs, the Americans are dogs, etc. It eliminates the hackneyed cliche of "treating people like animals" and it also makes you view the story with fresh eyes because it's told a little differently than usual.
As for style, I thought Spiegelman's style of story-telling was very similar to that of Harvey Pekar (of American Splendor fame), which is to say it's very common man, it's a little self-deprecating at times, it breaks the fourth wall on occasion...and something else intangible that I can't describe. I love Pekar's work, and I love this as well. It's hard to choose which parts of the books I liked most. The moments between the author and his father in the present are so realistic, rotating among frustration/anger at his father's irritating habits and attempts at guilt/manipulation, and worry/tenderness over his father's advancing age and physical/mental deterioration, and admiration for the strength and ingenuity his father had in order to survive the Holocaust.
On the other hand, the historical parts about Vladek and Anja in Poland and the many hells they went through to come out again alive and to find each other were so poignant and gripping - those were the parts that were impossible to put down. I'm still affected by this, two days after I finished the books - I have tears in my eyes as I type, thinking about all the people they lost, including their first son, and all the terrible things they saw, and what an unbelievable miracle it was that they both survived and found each other after they earned their freedom (because they were separated in Auschwitz and didn't see one another or hear from one another for a long time).
It's an incredibly moving story told in a somewhat unconventional manner. It has won several awards and a great deal of recognition. All well-deserved, in my opinion.