Zombie Edition is a mod based on original half-life concept, but you will play as a headcrab and, what is more interesting, as a zombie. Zombies can mutate to change their characteristics into three types and every type will have at least six upgrades including using new weapons and abilities. For further information please check this mod's Official Page.
First trailer. With Rusher. Just if you want to download it. Made by Stazz.
High-definition teaser number 2. Introducing... Crasher.
I don't know why, but good quality teaser was compressed badly by media uploading system, so I've decided to put it here.