There aren't many comedies about existentialism, and the brilliance of this movie is the way it uses the form of the screwball comedy to both represent and explore existential themes. The movie has a sure sense of comic structure and timing, with classic comedy conventions like high-speed dialogue, wild plot permutations, family craziness, over-reaction to trivial things, under-reaction to non-trivial things, some sharp satire about our consumer culture, a little slapstick, some terrible poetry, and of course a few romantic complications.
I Heart Huckabees is clearly the product of someone who has waded through teutonic philosophy and eastern mysticism and fortunately come out the other side with his sense of humor intact.
Director and co-screenwriter David O. Russell has a lot of fun playing with the classic philosophical dualities/debates. The difference between philosophy and art is that philosophy tries to deal with dichotomies in a logical and linear way, while art is free to ricochet back and forth between them like a pinball machine. Russell directs his crackerjack cast at top speed and they all perform with buoyant conviction and pure comic energy that is delicious to watch. This is Law's best performance so far, stunning in its fearlessness and control of tone. He keeps Brad a character and not a caricature, when he is at his most charming and when he begins to unravel.