It gets in your head.
The man who popularized zombies is now giving us their distant cousins; people infected with rage, to keep it simple. George A. Romero is pretty much living up to our expectations. In the case of The Crazies, he sets is action at a time when the virus is already widely spread. A lot of this film is a militaristic procedural that will split the audience. Basically, citizens are under martial law.
The central characters are two firefighters and a nurse. Both firefighters have served in the military. This puts them in a privileged position. They are both victims of the military and of the infected, but they have the background required to deal with both threats. Again, the deal breaker, here, is that this is a story of men versus to the government, not the infected.
Romero is a good storyteller. When he lacks the ability to craft suspense, he usually compensates with a good set of characters. The budget helps. It’s too bad so many actors are men. Not only does he scare away people who like more human experiences, he pushes away the female audience. Romero's work is an acquired taste and The Crazies is not for everyone.