Paul Giamatti's intense portrayal of "everyman" Pekar is both fascinating and disturbing. I'm a huge fan of Giamatti's; he brings a brooding desperation to the role. You can actually feel the frustration and hopelessness of Pekar's life.
Pekar found salvation by writing a comic about his everyday life. The movie is narrated by Pekar himself, with overlays of animation and cutaways to real interviews with Pekar. I felt these interludes were a bit distracting, but overall the effect was helpful in the telling of his story.
Snippets of the comic were acted out, then shown in the drawn form. Classic bits like Pekar catching a glimpse of himself in the mirror and thinking to himself, "Now there's a reliable disappointment" captured the man's outlook perfectly.
What I took from this story is the realization that there is real poetry and humor in even the most mundane human interactions, if you look at it with the right attitude. That's the true wisdom in this portrayal.