THROUGHOUT ITS HISTORY, television has been called the boob tube, the idiot box, a haven for “lowest common denominator” programming. Yet if this year’s Emmy nominees and the new TV season demonstrate anything, it’s how demanding episodic series have become — with all the associated risks that entails.The observation that TV shows have grown increasingly elaborate isn’t new. Indeed, Steven Johnson made this point a centerpiece of his 2005 book “Everything Bad Is Good for You: How Today’s Popular Culture Is Actually Making Us Smarter,” which argued that the complexity of primetime series and videogames — especially compared with the narrative structure of vintage TV — has transformed the idiot box into a “cognitive workout” for viewers. As Johnson observed in one interview, “I suspect what has happened is that the more interactive forms (of media) — the videogames and the Internet and other things — have played an active role in terms of enhancing our mental faculties. Television has caught up with that.” There’s no doubt the TV menu is vastly more challenging, given the sprawling casts and maze of subplots in HBO’s remarkable dramatic trio “The Wire” (which returns in September in spellbinding form), “Deadwood” (about to conclude a riveting third season) and “The Sopranos.” Broadcasters have taken up this gauntlet, from ABC’s “Lost” and Fox’s “24″ to heavily serialized new programs such as “The Nine,” “Jericho” and “Heroes.” Even comedies have joined in, with ABC’s “Big Day” and “The Knights of Prosperity” following ongoing plotlines throughout their planned seasons. All told, it’s a long way back to the day when figuring out which Cartwright would fall in love — only to have the lass tragically die or move away — on that week’s “Bonanza.” This drift toward more intricate programming is clearly a blessing to critics and viewers weary of the same-old same-old, but it comes with a certain built-in peril. Like any finely tuned electronic gadget, the more moving parts a show contains, the more chances for something to go wrong and send the gravy train tumbling off the rails. In addition, the engaged fan bases these series engender take perceived lapses in quality almost personally, as if producers and network execs had mugged a close friend. How else to explain the level of vitriol directed at the second season of “Desperate Housewives,” which got into narrative trouble by chewing up so much story in its maiden year, or the perplexing backlash against the recent flight of “The Sopranos?” Viewers seem almost eager to announce that something has “jumped the shark” — the popularized expression for when a program crosses the abyss from hit to has-been. Tellingly, though, that phrase refers to an episode of “Happy Days,” which continued another 100 episodes after that supposed point of no return without any resounding hue and cry at the time, largely because there was no Internet upon which to do one’s hueing and crying. In the not-too-distant past, key TV franchises could play for years with only mild deviation from their basic template. By contrast, modern serials are all but obligated to take chances that can pan out (“Lost’s” unfolding mythology) or not (“Nip/Tuck’s” “The Carver” plot). Producers have also embraced such risky storytelling, which explains why “Battlestar Galactica” blew up its existing framework in last season’s cliffhanger and “Prison Break” returned as what amounts to a completely different show — morphing from a slightly sanitized “Oz” into a multiheaded version of “The Fugitive.” One side effect here is that the evolving nature of these programs makes initial reviews less revealing. Pilots have always been a work in progress, but with such multifaceted concepts, the sundry characters and plots can coalesce into something wonderful or, more often, that will divert only a few dozen dweebs in a chatroom. Take a series like CBS’ “Jericho,” which opens with a small community sequestered from the world after a distant nuclear blast. Its initial hour is interesting, but it doesn’t betray much about how viewers will feel come October, much less season three. As a practical matter, this trend toward smarter TV has largely eliminated resting on one’s laurels — the notion that after developing a hit show, producers and talent can coast to the promised land of syndication. Today, that voyage is more like a turbulent ride through shark-infested waters — or at least, waters filled with those ready to accuse you of jumping one.