I saw this last night, and I'm not sure how I feel about it.
There was so little explanation or back story, that the whole "alien invasion" just felt like it was tacked on to the plot as an excuse to throw the characters together. I wanted to know so much more, but to the plot it was irrelevant. It could have easily been about a civil war, a drug war, a disease outbreak, or anything.
The two lead characters irritated me as well. He was just a selfish ass, and she a "poor little rich girl" rebelling against her father. I had no sympathy for either of them.
The cinematography was beautiful, however. And at no stage did the director break out "shaky-cam". Not even during action sequences. That made a very refreshing change to just about everything released since "Blair Witch Project." (Tripods, and gyro-stabilized cameras, I LOVE you.)