Green Arrow's not entirely unpopular. He's had his own comic for quite soem time, he's been on cartoons and live action television shows, has toys out, he's more popular than Blade or Elektra were when they got movies.
I don't doubt that he's not popular among the fanboys. I knew exactly who he was and I knew quite a bit about his origins when he appeared on JLU. I'm talking about the guy on the street who only goes to superhero movies for cheap thrills and maybe even a bit of substance. The Blade and Elektra comparisons don't work either, because they were an origin movie and a semi-sequel/origin respectively. In this movie, you're getting a character (who no average filmgoers will have heard about) who has presumably already established himself as a superhero/vigilante, and then before you know it, he's put in a nonsensical plot sans his superhero fixtures.
I think that is the point.
But he's non-powered. What's the point of putting him in a maximum security penitentiary for superhumans, if he doesn't have any powers? His skill with a bow and arrow doesn't count as a superpower, last time I checked.
I'd say its a good thing Hollywood doesn't care about Irish fast food.