The anime industry is a pretty rigid one. It takes time for talent to surface, people never start off by directing a movie of their own. Even major talents like Mamoru Oshii started their careers inbetweening children's cartoons. It's the way the industry works, and there's very little room for change. Yet there are some people who are talented enough to break right through these traditions.
Makoto Shinkai is one of those people. When Hoshi no Koe was released, many heads turned. Being only his second short film (and his first lengthy one), Shinkai directed a movie that not only had a unique visual style and was technically impressive, he did it all by himself. Without the help of any major studio or other animators, without prior experience in the industry, he created a 30 minute animated short film that equaled and surpassed many other professional efforts. No matter how rigid an industry is, this gets you noticed.
With Hoshi no Koe, Shinkai put his name out there. While not all the work was done by himself (his wife and a couple of friends did the original dubbing), the bulk of the work was all his doing. Though he directed a short film before, with Hoshi no Koe he defined his personal style and developed an atmosphere he could call his own, crafting it to further perfection in his later films.
The film is now 4 years old, yet it still looks lush. It's not the prettiest anime out there, not by far. The cgi looks pretty standard and the characters designs aren't really that good, but Shinkai knew perfectly well how to mask his shortcomings. By using strong, vibrant yet dreamy colors, applying a smart mix of 2d and 3d artwork and getting some good camera action he was able to fill each frame with a lavish setting that easily overshadowed the lesser points of his work.
This visual identity has always defined Shinkai in a way. While his movies always radiate a certain grandeur, it's always in function of small, romantic elements. He has always focused on the smaller things in life, voicing his admiration of them through his characters. The setting of Hoshi no Koe also reflects this. While in the background there's space travel and mecha fighting, the film is really about two people being separated by time and space, pondering about their time together. Thinking back of walks in the rain and spring mornings, seeing the cherry blossoms fall. That's Shinkai.
These conflicting elements never get into the way of each other, although a better focus might have improved the film a bit. Something Shinkai himself picked up along the way of his further career. The storyline functions as a mere setup, leaving all details and further explanations to a bare minimum. This makes the short a tad hard to follow, but in the end the atmosphere really benefits from this choice. The focus is kept on the theme of the film, instead of delving into a cliché setting not really worth exploring anyway.
Hoshi no Koe really is a landmark movie. Not only because it was the first good example of how increased processor power combined with a creative and persistent mind could penetrate a rigid industry, but also because it set the bar for Shinkai's individual style, which would only improve along the way. Not many people followed in his footsteps (although there are some examples, ranking them immediately among the best anime directors out there), indicating his rare talent.
With all circumstantial arguments out of the way, Hoshi no Koe remains above all a sweet, touching little short set to a rather violent and typical anime background. His later efforts would put both elements in better balance, but the effect is already here, and the short still stands proud 4 years later.