The Darkest Hour probably got green-lit because it's a somewhat unique idea (sidenote: also just about every alien-invasion movie these past couple of years were made after executives probably saw the numbers that District 9 pulled in). The film is about four tourists who are caught up in an alien invasion while in Russia, but the aliens are invisible and can only be identified by short, orange electrical beams of energy. Different design element in a foreign environment... could be something different. Turns out, the movie doesn't go anywhere beyond its setting and genre. Movies have been to Russia, movies have been made about alien invasions, and we have seen electrical currents captured on film before.
Throw in five basic character types consisting of two American tourists, two girls, and one foreign jerk and you have a movie that jumps from survival horror to science-fiction themed resistance fighting where the characters speak in cliches (almost as if they know what to say and do in a movie like this). Shame that a talented cast (Emile Hirsch, Max Minghella, Olivia Thirlby, Rachael Taylor, and Joel Kinnaman) are wasted as well as the talents of director Chris Gorak who was the main reason I know a few film buffs bit the bullet and saw this movie. This basically could've been his big-budget debut, but fans of his acclaimed (reasonably speaking) first film "Right at Your Door", will be disappointed.