Adam Elliot is one of my favorite animators, and I think every semester I've taken a class in animation I've had to watch his short film, Brother. I love how, even with very limited animation, he can create a sense of character and have an audience be able to empathize with them within minutes. And the same is true for Mary and Max. Even though it's a much longer film than Brother and there's a whole lot more puppet animated movement, the emotions that you feel for the characters are automatically felt through their character descriptions. There isn't too much plot in the story: if you strung together all of the actual storytelling parts it'd be an extremely short movie. But the fun of it comes from how interesting Mary and Max's lives and idiosyncrasies are.
And the look of the film is superb! There isn't much color used at all, mostly monochromatic colors and the occasional red when Elliot wants to make a point out of something rather important and/or sentimental (such as the pom pom that Mary makes for Max that he wears on his yarmulke and the portrait that she draws for him).