1. Before Watchmen
Green Lantern/Green Arrow is important for a whole host of reasons, and as far as legacies go, they don't much greater than its own.
There are plenty of events that marked the beginning of the Bronze Age of Comics - Gwen Stacy's death, for instance, is optioned as a key one - but the book that made it was O'Neil and Adams' seminal seventies hit. Green Lantern/Green Arrow was bold in its premise and even bolder in its delivery, rooting itself squarely in the malaise of the early seventies and questioning DC's own history in the process of doing so. It challenged the genre to be more, and while that isn't to say that it's a perfect book (it isn't), it did kickstart a whole wave of comics that felt brave enough to approach the real world; Marvel did so in Steve Englehart's scathing critique of Watergate in 1974's Secret Empire, and further forays into contemporary politics became the hallmark of the Bronze Age's closing moments, leading to the Modern Age of Comics with the ascendancy of Frank Miller, Alan Moore, and the British Invasion.
But perhaps Green Lantern/Green Arrow's most enduring contribution to the world of comics lies in how it redefined the DC Universe. Once considered unadventurous and sentimental, O'Neil and Adams dragged that world to be something bigger altogether, proving that it's not geographic analogues that reflect the world outside your window, but rather the issues that define it. Marvel's role in galvanising this change is of key importance, but in going one step further, both publishers deserve equal praise in challenging the medium to be more.
More innocuous, however, is the way in which GL/GA redefined two of DC's most prominent figures. They may lack the appeal of Batman and Superman, but the image of Hal as a rebellious do-gooder is now etched into the fabric of the character, as are Green Arrow's radical politics and goateed appearance.
In any case, Dennis O'Neil and Neal Adams' Green Lantern/Green Arrow is one of the most important comics of all time, and DC's definitive Bronze Age work.
What do you think is the most important comic book of all time? Be sure to let us know in the comments below!