The movie has the longest opening sequence ever. I mean the title and opening credits don't start until about 45 or so minutes into the movie! We have a Japan cut in half like in the movie Doomsday, but instead of a deadly virus we have a horde of zombies.
The zombies all have horns which apparently can be used like a drug when ground up and snorted like cocaine, but unfortunately it is also highly unstable like nitroglycerin and if improperly handled.....well you get the ideal. Zombie horn poaching is therefor illegal, but also quite lucrative.
Zombies can not be killed via head shot alone either. They need to have their horns removed. A head shot or decapitation won't totally kill the zombie. The body parts of the zombie are still "alive" could be combined with other zombies body. A spider zombie and a zombie car are a couple of the fun creations that can be made.
The primary feature of the horns are that they are a control rod for the main zombie. This feature is not apparent until later in the film when then zombie "Queen" uses her horn to control the others. She uses the zombie combination feature to make a giant zombie which is then morphed into 747 to try and flow outside of the quarantine zone.
Final thoughts: Awesome. This movie is full of fun bits and lots and lots of gratuitous blood.
Addendum: Where else can you see a guy sword fight a sword zombie with his pickup truck? No where! What this movie!