Pretty cool and convincing until...
...the main reporter chick turned into a typical horror-movie stereotype. She was fine for the first hour and 15 minutes, but once she got into the test-tube apartment, suddenly she wouldn't shut up, kept screaming and hyperventilating, wouldn't listen to her friend, etc. The whole movie, I wanted her to survive, but at the end, I was dying for someone to bite her and stop annoying me.
In the director's other excellent movies, Devil and As Above So Below, there was just as much fright and intensity, but without an annoying character like that.