**SPOILERS** You know what would have REALLY surprised me at the end?
Is if the two of them had escaped, the credits rolled, and there was no indication whatsoever that the infection had spread elsewhere. It really would have shocked me if they hadn't shifted the camera to the satellite view and shown that the government was planning another quarantine, or if they hadn't shown the little news clip during the credits.
I know, the effect is supposed to be "Oh no! It's not over! How sad!" But for those of us who've seen dozens of horror movies, the effect is really more like "Oh, God! Does every horror movie have to end the exact same way?"
It was still better than I expected, though.