You see bits and pieces of "The Happening" and "28 Days Later" - a mysterious toxin is causing the zombie-ism. "The Crazies," though, dates back to 1973, and is actually a remake of an obscure George Romero movie.
If this strikes you as a red flag, I feel your pain. Hollywood's made a mint in recent years with slick, cynical remakes of disco-era horror brands, and some of the same people are involved in this update.
"The Crazies," happily, turns out to be better than that bunch, elevated by a good cast, sincere treatment, and direction that favors atmosphere and pacing over envelope-pushing sadism.
There is no bogeyman to celebrate (or market), and characters register as much more than likely victims. Olyphant is highly sympathetic as the sheriff who tries to maintain order in a town rapidly losing its collective grip.
When that fails, he simply tries to protect his pregnant wife (Radha Mitchell). Joe Anderson makes a nice impression as the deputy sheriff who helps the two find a way out of the bloody, bonkers town, which may become the site of a ruthless government quarantine.
Federal intervention gets a little heavy-handed, and you keep expecting the movie to register some anti-government vibe or theme. "The Crazies," though, seems to be focused solely on old-school kicks for genre fans and delivers.