Garrison Fox’s review published on Letterboxd:
Don Hertzfeldt's It's Such a Beautiful Day is a collection of three short films about Bill, a psychologically troubled figure who slips in and out of reality and ruminates on physical deformation and death. The film isn't necessarily special for its story, but for how its story is told aurally and visually. Hertzfeldt's animation style is just as fragmented, claustrophobic, and impressionistic as Bill's perception of the world, and it's made even more engaging by Hertzfeldt's narration and an orchestral soundtrack. I did a little research on Hertzfeldt but failed to find any personal health problems. Nevertheless, it would not at all surprise me if he suffers from something because his films are morbid, frightening, and even profound. Beautiful Day almost seems like a coping mechanism or a means of catharsis for a life of dysfunction. Whether or not that's true, it's an innovative, deeply unsettling, disturbingly funny, essential animated picture.