I'm a shader-whore, so here goes:
(I know eye-candy comes last for a game, but most other things have already been mentioned)

- The bullet effect in slowmo looks cool, but you clearly see it's just a cylinder with a refraction shader once you move around the effect. You can do better than that, i know it Maybe add an inverted velvety shader and use that as alpha?

- As already mentioned, the zombies don't really fit the overal style, the lighting is too toony and looks flat. I don't know if normalmaps are supplied with the modelpack, but if you have them, use them. Add a shader which adds normalmapping for detail and better lighting, (little) specular lighting and velvety for depth, environment mapping so the limbs look as if they are still wet of blood. Maybe you could add a little refraction to the limbs instead of environment mapping, as you already have the refractmap for the bullet effect? This could actually look better and more "wet" than environmentmapping.

- Add shadows. There is no better method (besides sound) to add athmosphere to a zombie game. Either use A7's accelerated stencil shadows with LOD or a shadowmapping shader. I think that would add a lot to the overall look and athmosphere

- You have a refractmap, maybe you can also use it to spice up the explosions? That way you also get fake soft particles and a more firey look, if done right.



Looking forward for more vids!