Elektra was one of Marvel's modern early attempt at a superhero movie. I say modern, because there are some deep cuts of Marvel superhero movies, like the '80s Punisher movie. Nobody knew what to do with superhero movies back in the 80s. It wasn't until the 2000s that the genre came back. Elektra may seem like a weird choice, but this was back when they were too scared to try their bigger names in fear of ruining them. Obviously they are over that fear now. They're throwing these movies at us like bread to ducks.
Elektra was a character from the Daredevil world and they were trying to ride the Ben Affleck Daredevil train. Unfortunately that train was more like one of those trains meant for kids. Slow and lame. Garner was a good choice for the character though, given her experience on 'Alias' as a butt-kicking spy.