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 new weapons and abilities. For further information please check this mod's Official Page.
This mod has a lot of potential. But I feel like it didn't live up to what it sounded like. The maps aren't the greatest and the AI is horrible, but it just didn't get enough attention for them to continue. They completely stopped making updates for it, and only now are they updating this page, but only because it got added to Desura. I give this a 6/10. Would be amazing if it was still in dev.
One of the best mods, but with some imperfections. The idea of playing as a Zombie and an Headcrab is great and there is an interesting RPG System to change your classes and upgrade your powers. The mapping is quite good and looks like Black Mesa. It has a good atmosphere and exciting battles, they are quite hard and you need to use your skills there! Black Mesa Personnel, including Barneys and Scientists, use strong weapons too now. Barneys use even Shotguns and Combat Rifles while a few Scientists use Pistols. As a Zombie you can have Special Powers and certain Classes and you can also grab Headcrabs from the floor and throw them at your victims. As a Headcrab you can even use a nice Stealth System to sneak past your enemies. However the new Models were simply horrible: why did the Creator include those horrible PS2 Models in the mod? I hated them. That's why I lowered the rating of this mod.