I've been watching Six Feet Under again (finally...holy shit, and I'm progressing through season three), and I've had a revelation. Michael C. Hall should be the Green Lantern.
Michael C. Hall is the titular character of Dexter, but I'm only familiar with him as David Fisher on Six Feet Under. David's my "favorite" character (I use quotation marks because you really "can't" have a "favorite" character on Six Feet Under...you'd have to watch to understand), so maybe I'm slightly biased.
Nonetheless: director Greg Berlanti should forget about the rumored Bradly Cooper and tap Michael C. Hall. We can begin just with his physicality. Hall's eyes are green (not clearly green, but Cooper's are bright blue); it's kinda gimicky, but Hal Jordan's eyes are green in just about every portrayal I've come across. And Hall doesn't have the body of a Greek god, but the athletic build is there. He can work on it. I also think you can see Hall in a flight pilot jacket and an emerald green mask a lot better than Cooper. The former would look like a respectable and admirable superhero and the latter might look like a crowd-pleasing pretty boy. (Photoshop, anyone?)
More importantly, as far as physicality goes, what I like about Hall that I see in Six Feet Under is that he can definitely be charming, but when he's serious, he pulls it off like a heart attack. He also brings a subtle physicality to repressed internal conflict and emotion; you can tell if he's embarrassed, hurt or suffering from indigestion just by the way he shuffles his feet or fidgets, or the way he frowns, but not in unrealistically dramatic ways. You can actually believe that he's fearless in some situations and that he's terrified but brave and putting on a fearless face in others. Hall can strike an oddly poetic balance between the two. (Yeah, "poetic." Work with me here.)
Hal Jordan is always drawn with the aesthetic of an American god, with fine brown hair, completely square jaw and chistled muscles. He's known as a man without fear, and he is, but he also struggles with being afraid of one thing - actually being fearless and what kind of person he could become with his unlimited power as the greatest Green Lantern in the universe. He doesn't express his internal feelings very often (unless he's blurting them out). The loss of his father, and the subsequent impact it had on the loss of his mother, make for some interesting Freudian shit. Beneath his Herculean exterior, Hal Jordan's past and his conflict with his own will to power make him interesting. So he needs an actor who will play someone who's clearly mythological but bring in enough subtlety to make him believably human, too.
Seeing Hall in interviews, I think he pays close attention to the psychological processes of his characters and tries very hard to make their responses to situations as authentic as possible. From what I've watched of Dexter, I think Hall's also very aware of how to get certain responses from an audience that both wow you in a "It's only fiction" way and yet make you believe the character could be a real person. Whomever plays Hal Jordan needs to bring this sensibility to scenes like finding a dying alien in the middle of the desert, discovering that the universe is overseen by a group of short blue guys, and reciting a sacred oath to recharge his ring. It requires a fine balance between taking the role seriously and having a ton of fun with it, and Hall seems capable of striking such a balance (again, "poetic" - work with me here).
Berlanti can save Bradly Cooper for later; Cooper's repitoire suggests that he might be better suited to play Guy Gardner - the more cock-sure, womanizing and arrogant Green Lantern. But Michael C. Hall has a more solid acting career, I think, than Cooper. He's just basically kinda perfect for the part. Michael C. Hall for the win!
Can you see it? Yes, of course you can.
...P.S. As long as I'm admitting that I've recently started watching Six Feet Under again, if the powers-that-be settle on John Stewart instead of Hal Jordan, we oughta try to get Keith's actor, Mathew St. Patrick. He's a fantastic actor who can balance good humor, intimidation, vulnerability and rage all in one performance (at least on the show), which pretty much describes John Stewart. Plus he's huge and doesn't make being bald look stupid.
...P.S.S. NO, I do NOT secretly think Hal Jordan and John Stewart should get together. Really, I don't. David and Keith belong together only on Six Feet Under, and I didn't know until tonight that Berlanti is gay. ...Interesting coincidence, though.