If you've not heard yet, the movie is quite infamous. Because it goes places (especially visually) that may be a bit too much for some viewers. As others surely have pointed out, the idea is not new. And you won't really see too much of a story here. Actually you may wonder if what we learn from the relationship that our two leads have, was in any way essential or necessary.
But before the mayhem begins, it is always nice to have some... well quiet time. Also the beginning clearly is a statement - to all the conspiracy theories and to how the world has gone mad. Quite a few stabs at things going wrong - politically but also socially speaking.
That is not the only thing you get though. Apart from the overall plot being lifted from something like The Crazies by Romero, you also have homages to a lot of other scenes from many different movies. Irreversible, Night of the Living Dead, Serbian Film and so forth... I reckon a second viewing would reveal even more to me.
As it is, this is no holds barred, mostly practical effects violent splatter fest... take it or leave, just don't judge for something it isn't.