Floyd Lawton, way back in the early days of Batman comics, was inspired by stories of Batman to put on a tux, a domino mask, grab two guns, call himself Deadshot, and fight crime. In an effort to become the public's preferred protector of Gotham, he launched a campaign to paint Batman as a bad guy. The lesson, as always: don't piss off Batman. With Jim Gordon's help, Batman uncovers the plot to run the Dark Knight out of town so that Deadshot can take over organized crime in the city.
After spending some time in jail, and I think being mostly forgotten by comics writers, Deadshot re-brands himself as an assassin for hire, and equips himself with two pistols mounted on his wrists and a scope built into his mask. Since he's one of the best marksmen in DC comics, his services are in high demand.
The most unique and interesting aspect to the character is his lack of a self-preservation instinct. He's not suicidal, but the idea of going out in a blaze of glory is appealing to him. He's also been shown to have an odd code of ethics, where once he's been paid for a job, he feels responsible to carry it out. So in a pinch, he has no problem putting his own life in jeopardy if it might mean getting the job done.
Pros: His borderline death wish creates a lot of possibilities for dramatic action sequences, and he's certainly a different kind of antagonist than we had in The Dark Knight.
Cons: The scope mask and guns is the sort of comic book idea designed for your inner adolescent (or actual adolescents), which is the sort of thing these films seem to shy away from, preferring to try to pry adult drama out of the Batman mythos. Also, if you had a scope mounted to your eye, would that actually work? You mount the scope on the gun, because that lets you see where the gun is pointed. With the scope on your eye, it tells you where your eye's pointed. Which you should already know. Maybe that's been explained somewhere, I was never a big Suicide Squad reader, which is where Deadshot has made the bulk of his appearances.
How I'd do it: The death wish angle would have to be the focal point. Without killing him, how does Batman stop a killer who would much rather die than be stopped? Unless someone can explain the scope thing to me, that might have to be dropped, or at least changed to plain old night vision. And I'm not sure two guns would play well either. John Woo action would seem out of place in this world.
Casting Guesses: I honestly don't recall what Deadshot looks like under his mask. So he could be played by literally anyone. I'll throw out Karl Urban's name. He's pretty good at playing assassin types.
Verdict: Another guy who will certainly not be the main villain, but he could be a secondary one, or even just make a cameo.
After The Scarecrow, Ra's Al Ghul, The Joker, and Two-Face, who should be Batman's next enemy in the Batman Begins/The Dark Knight series? Well, as of now we know that Tom Hardy will play Bane and Anne Hathaway will play Catwoman.
Check out the master list for all the villains covered. I've pretty much run out by now. Obviously, there are more Batman villains, but not any of significance that I know of. As of February 2009, no one is confirmed as a villain. Not the Johnny Depp Riddler, not Phillip Seymour Hoffman Penguin, nobody.