We don't exactly know at this stage who Hirsch will be in the film, but it's probably not much of a gamble to assume that he'll be playing one of the Americans trying to survive the alien attack on Russia versus one of the aliens doing the actual attacking. Whatever role he's in, I really like the direction this cast is heading. Right at Your Door proved to me a lot of things about Gorak's directorial command, but chief amongst those was his ability to make a film about the characters and ideas over special effects. So while Bekmambetov has consistently shown that he is all about the latter, I have a feeling Gorak is going to shape The Darkest Hour into a District 9-esque sci-fi film that downplays the spectacle in favor of the characters.
Obviously that's all assumption at this point. I haven't read the script - which Variety attributes to Les Bohem and Jon Spaihts, while The Hollywood Reporter notes Gorak and Josh Zetumer have taken it over - so it may be more in line with Wanted and the Night Watch franchise, but I'm holding out hope that it's not. District 9 and Monsters have me jonesing for more character-driven alien invasion films, so it'd be nice if The Darkest Hour kept that trend going.