This is, to put it plainly, one hell of a time to be a comic book nerd.
All my favorite characters(*) are making the leap from the page to either the big or small screen. Marvel can seemingly do no wrong with its film output, turning an obscure and downright goofy property like "Guardians of the Galaxy" into one of the year's biggest and most beloved hits. TV's most popular comedy ("Big Bang Theory") has a comic book shop as one of its primary sets, and a main character often seen in Flash and Green Lantern t-shirts. TV's most popular drama series ("The Walking Dead") is based on a long-running comic book, and there are currently five other comic-based shows airing on the broadcast networks (ABC's "Marvel's Agents of SHIELD," FOX's "Gotham," NBC's "Constantine" and the CW's "Arrow" and "The Flash"), with more coming fast. (The CW has "iZombie" set for mid-season, Netflix will premiere four different Marvel series over the next four years, and adaptations of "Supergirl," "Preacher," "Lucifer" and more are in development.)
(*) Okay, maybe not my personal favorite Wonder Man, whom Joss Whedon said was basically the only Avenger he never wanted to put into a movie because, "I never did figure out what he was for." My retort would derail this column, so let me simply point to this gif I made, featuring Wondy in the greatest of all his interesting costumes, along with the broad pro-Wonder Man argument.
These shows are becoming so pervasive that at Thanksgiving dinner, a cousin who reads my blog complained, "You need to stop writing about so many comic book shows."
Comic books were, once upon a time, a mass audience product. At the peak of the medium's popularity during World War II, every boy, girl and G.I. Joe in America knew all about Superman and Batman. Eventually, though, they became a niche product, where an adaptation in a more mainstream medium — say, the campy '60s "Batman" TV show — could for decades define public perception not only of one character, but comics as a whole.
That's why the huge success of the Marvel films (and DC's attempt to imitate them by using the next Superman movie to jumpstart a Justice League franchise) has been so improbable, and so cool from the perspective of a lifelong fanboy. It's not just that so many of these films are huge hits that cross multiple demographic lines, but that they cover so many genres and tones, tied together mainly by the Marvel logo at the start of each film. They've taken something that was culturally marginal and made it very mainstream again, and it's easy to understand why the TV business in turn has treated comic books as the new gold rush territory. 
The hope was that these comic book shows with their familiar heroes and/or brand names could quickly find a mass audience in a fractured landscape where almost no new series does that anymore. But the one major commonality among all the current broadcast network comic book adaptations is the way they demonstrate that on television, comic books and superheroes are still very much a niche business.
Now, "Arrow" and "Flash" are two of the biggest hits the CW has ever had, and "Gotham" is FOX's biggest hit of the fall. But those successes are all relative, because the CW has such a small audience base to begin with, while most of FOX's schedule this fall has been a dumpster fire. NBC declined to give "Constantine" a full-season order (though there's still a chance it could get a second season), and "Agents of SHIELD" ratings are a fraction of where the show started last year. Just in terms of total live viewership, all these shows finish well behind the ongoing saga of that police superwoman CopMom MomCop (aka "The Mysteries of Laura"). And when I walk around in my Flash t-shirt these days, I get smiles and compliments, but almost always from "Big Bang Theory" fans ("Awesome Sheldon shirt!") oblivious to the existence of the CW show.
There's nothing wrong with that, by the way. The anomaly has been the sweeping popularity of the comic book movies, not the more modest success of their TV counterparts. Comics are a niche market, and television has become a business of niches as well, with the likes of "Walking Dead" or "NCIS" — which soundly thumped "Agents of SHIELD" when ABC pitted the shows against each other last year in an act of scheduling hubris — growing increasingly rare. A comic book show is the exact kind of project a lower-profile network like the CW should have been trying, and executives there are rightly over the moon with how "Arrow" and "Flash" have done.
And creatively, these shows (even the mighty "Walking Dead") have done their best when they haven't pretended that they can be all things to all people — and also when they've kept things relatively focused.
Not that any of its lost viewers have returned to notice, but "SHIELD" has turned from a bland procedural with vague superhero trappings into an entertaining and confident serial. It's finally taken advantage of its lower profile by having fun with some of the less in-demand characters and concepts from the vast Marvel Universe, whether with a convincing take on the Absorbing Man or Adrianne Palicki instantly taking over the show as Avengers C-lister Mockingbird. This used to simultaneously feel like a show mainly interested in brand extension (Here's what happened to that thing that fell to Earth at the end of "Thor: The Dark World"!) and like one ashamed of its own comic book origins; now it's gotten much better by concentrating on its own characters and stories, while celebrating whatever toys are available to it.  
"Arrow" also took advantage of the relative obscurity of its main character, which gave the writers the freedom to try any approach with him without upsetting their corporate bosses' larger media plans. Green Arrow's more important to the Justice League than Mockingbird is to the Avengers (he's a B-lister, at minimum), but still not someone who's likely ever going to be invited to be in a Zach Snyder movie. DC at the time didn't want to make a Batman TV show (and arguably still doesn't, but we'll get to that), but with Green Arrow — a character who began life as a shameless knockoff of the Caped Crusader — the creative team tapped into the character's origins as an imitation Batman to make what's essentially a Dark Knight series in everything but name.
And because that creative team (which includes longtime DC writer Geoff Johns) had a while to work out all the kinks, "The Flash" — more technically ambitious, and with a lighter and more optimistic tone than "Arrow" and the various Nolan/Snyder films — was able to (pardon the unavoidable pun) get up to speed almost instantly. These are two shows that don't require a PhD in superhero comics to follow — though there are plenty of Easter Eggs for the well-studied — but nor is there any of the embarrassed throat clearing whenever the source material gets too out-there. One of the "Flash" supporting characters, Cisco, is essentially an audience stand-in who asks nerdy questions about the limits of Barry's powers and comes up with colorful names for all his villains. (And, as a hat-tip to Sheldon Cooper's fashion sense, Cisco has been shown wearing a Bazinga! tee.)
Alan Sepinwall has been reviewing television since the mid-'90s, first for Tony Soprano's hometown paper, The Star-Ledger, and now for HitFix. His new book, "TV (The Book)" about the 100 greatest shows of all time, is available now. He can be reached at