This show shocked me by being one of my favorite shows of all time. Hidden underneath its extremely cartoon and "geared for kids" look, the show actually gives you a wonderful in depth story and a great world. But of course the real charm here is the chemistry between all the characters. Finn and Jake's relationship becomes something unforgettable to the viewers which never gets old after all eleven seasons.
Not only made of wit and charm, but also moments of deep introspection on far more abstract ideas pertaining to life, existence, war, love, time, family etc. than a cartoon would usually present to children, which sets this series so far above all of animation. Mix that with lovable characters, detailed arcs, an otherworldy, avant-garde electronic score and meticulous, psychedelic animation and we have a masterpiece.