Anime adaptation of Junji Ito’s excellent horror manga Gyo that is not quite as accomplished in terms of art direction (it’s okay, but cannot compare to Ito’s style and it looks more generic, while the animation quality is so-so), but due to the unique core concept is still worthwhile to watch. While the adaptation follows the structure of the 2-volume manga in broad strokes, it does something clever by inverting the relationship observed in the manga.
There Kaori became infected and Tadashi was trying to save her and ended up following her around, while the world was slowly going mad. In the anime version, Kaori is searching for Tadashi, who later becomes infected and transforms into something hideous. The anime adds some other characters as well (none who get out alive) and has a few unique scenes (the plane landing or the subway crash) while still following the plot template from the manga.
While not looking as creepy and weird as the manga, instead offering bright colors and less refined character designs, it still cool to see zombie sharks walking on land and become machines of destruction as they reign the streets of Tokyo, while swarms of smaller fish and even other sea creatures (a squid) roam around and threaten the population.
It’s gory, it’s bloody, extremely violent and often just disgusting. For all its flaws, you don’t see something like this very often and I can only recommend it for any fan of horror (read the manga first, though, its better).