The film could've just as easily been a terrible flop. The film doesn't have a particular story or character to fall, just several short stories with reoccurring characters. The reason why the film works out so well is because it has a particular style to it, and what really contributes to the film's style is the animation in the film. The film was shot with a mixture of built sets and green and blue screen. The result is lively characters interacting with their environment, but the backdrops have a flatter feeling to them. Rodriguez and Miller decided to use a heavy amount of animation for the film so that the look of it can resemble what was drawn on the page. The film has a very noir and surreal look to it while also looking pretty realistic.
The backdrops look fantastic animated, but the animators didn't stop there. They also cleverly enhanced the characters appearance with computer animation as well. The character, Kevin is a great example of computer animation being used on an actor. Elijah Wood is in costume, but effects are used to darken his face, and place a pair of glowing white animated glasses on his fate. The animation is used in simple yet brilliant ways to produce images that wouldn't be possible if shot practically.
Colors are played with a lot throughout the film as well. White silhouettes, black and white footage with colorized elements, shadows on faces, vibrancy, ect. It's all simple techniques that make a huge impact on the look and feel of the film. Unlike most films that waste time and money on more realistic looking effects, the animators in the film went for a very loose and fun style, echoing of film noir. I still can't stress how impressive the film looks for being constructed with simple yet effective effects.