Just to get terminology straight, I'm talking about the Iron Age of comics, an era distinguished from the Gold, Silver, and whatever the current age is supposed to be called (I've heard "Modern," which is doomed to inaccuracy in a few years, and "Electrum" which might be an inside-baseball joke among nerds).
The Iron Age is roughly defined as beginning sometime in the early 1980's and ended around 1996 with the bankruptcy of Marvel Comics, although vestiges of its influence still kick around in the comic book universe today. The high points of the era are often cited as works like Frank Miller's The Dark Knight Returns or Alan Moore's Watchmen. The low points are often associated with names like Rob Liefield. Hand-in-hand with the Iron Age was the collectibility craze of comic books with speculators and comic book companies simultaneously engaging in a mutal delusion that comic books of that era had tremendous value apart from reading them that was defined by foil-enhanced pre-bagged variable covers and the like. Wizard magazine was the vehicle for a lot of that, a self-fulfilling prophet which would write articles about what was red-hot then post price guides that proved that they were right.
Apart from the financials of the industry, the Iron Age was often characterized by a gritty, realistic deconstruction of the genre with a frequent emphasis on violence and a critical study of the personality of the characters. That deconstruction was largely post-modern in its blurring of the lines of traditional morality and often plumbed the crypto-fascism and the violation of the social contract inherent in the notion of a masked vigilante/superhero. The aestete of the Iron Age frequently involved guns, leather, sex, mysticism, and pseudo-Asian orientalism (aka "ninjas").
Over the last week I encountered two artifacts of the Iron Age: the Suicide Squad movie and the roleplaying game Cold Steel Wardens. There are a gazillion reviews for the Suicide Squad out there but I'll just say that it included practically all of the signifiers of the Iron Age I mentioned above, including a style-over-substance issue. I liked the original Ostrander series and am currently collecting the various graphic novels, mostly to appreciate what was happened historically in that title. It was one of the real germinating seeds of the Iron Age, especially when you consider that DC's other popular offering at the time was their hokey-jokey self-satirizing Justice League International (which I will freely admit to loathing with a passion and will expound upon another day).
For me the real intriguing Iron Age artifact is Cold Steel Wardens. Most superhero RPG's acknowledge the Iron Age with a certain amount of embarrassment, Cold Steel Wardens (I'll call them CSW from here on out) embraces the genre with gusto, although their version of the Iron Age is narrow. This isn't a game that will allow you to play Youngblood, Brigade, or any of the other titles best identified with massive guns and oversized shoulder pads, but rather with the low-powered, street-level superheroes like Batman or Daredevil. In fact, while CSW has superpowers in the rules, they are extremely expensive and can not be taken to the level where a PC can throw around tanks or have bullets bounce off their chests. The game explicitly states that powers can not negate the peril of mundane firearms or ordinary henchmen, citing both a need to maintain the genre and having the in-game suggestion that high-powered superheroes either don't exist or are quickly snapped up by secretive organizations. The emphasis on skills and basic weapons is so prevalent that the game rightly states that you could drop the powers entirely and run the game without them as regular crime fighters.
Along with the cap of superpowers, combat is deadly. A PC can not take on a group of armed thugs just by wading into combat--you'll need to use stealth, tactics, and maybe even a little dirty fighting to survive. Part of the combat rules involves the use of long-term injuries, both physical and mental, that a PC can suffer as a result of grievous injury. There's an illustration in this section of a bleary-faced masked hero gazing into a mirror as he tapes up his injuries that captures both the genre and the rules perfectly for this section.
There is an extensive section on investigation and a nice primer for GM's looking to create workable mysteries into a superhero game that even if you use nothing else from this RPG could be ported into almost any other game.
CSW is also very dark in theme. The pre-generated campaign features a grimy city wracked with crime that looks like Gotham and Detroit had a baby which was then abandoned in a dumpster. Some of the stories presented in the biographies of villains and heroes may push the boundaries for some groups. For example one superheroine is the victim of a gang rape, while one of the villains specifically targets children for murder (using a classically benign superpower in a particularly grisly manner). Given the age range of my own gaming group, I'd probably dial this down a notch or two.
I've often thought that superhero RPG's really failed to allow for skill-based or low-powered superheroes that are a staple of even high-powered superhero comic books. Many times the skill systems were so underdeveloped as to be an afterthought (aka Marvel Heroic Roleplaying). Cold Steel Wardens has something like six skills dedicated to investigation-related tasks alone, e.g. Canvassing and Forensics. This would be a great system to use if you were trying to replicate the feel of Detective Comics or Batman Eternal, or television shows like Arrow, Agents of SHIELD, or Alphas where superpowers are toned down. I'm not sure this a game for every group, but it at least tries to give its audience the best of what the Iron Age had to offer without all the eye tattoos and bizarre anatomy.