One of my favorite parts about Maus is the "realness" of the characters, and I think having both likable and not-so likable aspects to each character is vital in creating a persona that could exist in real life.
Vladek is pretty stereotypical in a lot of ways--he won't spend much money and he won't throw anything away. This is quite characteristic of how my grandfather was. Granted, my grandfather did not live through the Holocaust, but the fact that Vladek can remind me of someone in my own family automatically made him more relatable to my own life.
The way he treats Art (especially in regards to throwing away his coat) and the way he treats Mala are not likable characteristics, however. He seems to always be mentally comparing Mala to Anja, and Mala definitely cannot compete with his first love. He makes her out to be an awful wife, when really, I think she just never had a chance to begin with. He doesn't seem to listen to his son (in regards to his coat, his wife's diaries, and other things), but there is a certain dynamic of their relationship that I can understand. I can only imagine it is difficult to talk about the Holocaust in great detail for your son, and so purging all memories of that from the outside (like burning Anja's books) makes sense in a lot of ways as attempting to erase the past as he is recounting history.
Though Vladek appears to make himself smarter and wiser than everyone else in his story, this did not bother me or sway me on my opinion of his character, as I would expect there to be some bias in a personal story. It also reminded me of the way my grandfather used to tell stories--he was always smart, brave, and cunning, causing him to escape all trouble. It had a nostalgic feel.
Art is likable in the sense that he wants to know his father's story. He is curious, he is an artist, and he's also incredibly relatable. Just like the rest of us, Art gets embarrassed by Vladek when they're publicly seen together. I found this humorous, as I'm often infuriated and annoyed with my parents as well.
The times I liked Art best were when he was reflecting on his own past. His comic about his mother's death was incredibly moving, jarring, and disturbing all in one go, and it gave him more depth as someone who is still trying to understand why his mother would leave him like that. He has many emotions, and he expresses everything from pain to happiness.
Art also has a way of coming off a bit forceful with his father. There are times when Art really just wants to get the story out, and I don't think he's taking into consideration how difficult it could be for his father to recount the most trying and difficult time in his life, especially since it also brings back memories of his wife.
To me, a story has much less impact if I can't relate to any of the characters. I think that this is true for many readers, as I don't make an investment in a book that I can't put parts of my own life into. This story holds a lot at stake for me, and it's one of the most personal and compelling Holocaust stories that I have come across (which is a lot, high school happened). It doesn't matter as much to me if I like a character as long as that character has human aspects that I can understand and relate to, and Vladek and Art are quite human for appearing as mice.