Arrow is, at its core, an origin story, despite the fact that Oliver appeared fully formed as Green Arrow from the pilot episode. However, he's NOT technically Green Arrow yet, and has to "earn" his heroic moniker. When he debuted he was simply called The Vigilante and The Hood. With time, he began getting called Arrow, and now he's just one word away from taking his true title. It's a minor detail on paper, but thematically it's incredibly important. Over the course of the series Oliver has learned to stop killing and become more of a hero than a vigilante. The city has gained his trust and even the cops have stopped hunting him. Pretty soon, he'll begin to resemble his comic book counterpart and really come into his own as a superhero. Origin stories are nice and all, but we're really here to witness Oliver's ascension and the fact that it's so close is extremely exciting.