Is it time for ‘Walking Dead’ to kill Rick?

“This isn’t life!” someone complains during “The Walking Dead” mid-season premiere (Sunday at 9 p.m. on AMC), objecting – as so many characters on the zombie series have over the last three and a half seasons – to the point of continuing to exist in such a miserable, disgusting, hopeless world. If the best anyone can hope for is brief periods of subsistence punctuated by terror and the sight of your friends being eaten and transformed, why go on?

For the most part, viewers haven’t been troubled by this question. “The Walking Dead” remains the most popular non-sports show on television (at least in the advertiser-friendly 18-49 demographic), as unstoppable as one of the zombie herds that frequently menace the main characters. (A few times in the fall, it out-rated “Sunday Night Football.”) The series has pushed out its two previous showrunners, and the ratings have only gone up. It’s killed off major characters, and the ratings have only gone up. The public appetite for zombie mayhem is so insatiable that the only living person, on or off-screen, who may be wholly irreplaceable – and that includes writer/producer Robert Kirkman, whose comics inspired the show – is producer, director and gore makeup master Greg Nicotero.

People love their zombies, because as the show kicks off the second half of its fourth season on Sunday, it’s hard to imagine them loving most – or even any – of the human characters, let alone wanting to go on and on with them if there wasn’t the constant threat of something very gross happening to them.

There are things “The Walking Dead” does incredibly well. The show has an unflinching sense of dread, even during the relatively peaceful periods, and it consistently finds creative new approaches for the macabre zombie attacks that tend to be the highlight of each episode. (Even the fall’s worst installment, in which it was the Governor’s turn to ponder the meaningless of existence, had a terrific, darkly comic set piece at a nursing home where he was set upon by zombies whose parts didn’t work any better in death than they had in life.) It even, at times, is capable of delivering great emotional moments, but they tend to involve guest stars (like Lennie James’ Morgan, who hopefully will return at some point now that AMC has canceled “Low Winter Sun”) or characters who are about to die (Lori sacrificing herself for the sake of her unborn child, Merle having a moment of clarity before going solo against the Governor’s men).

The problem – from a creative standpoint, if not a commercial one – is that most of the remaining characters are so flat and lifeless that it wouldn’t be the least bit troubling if any or all of them got bitten by the walkers. And the least interesting of all at this point may be the show’s chief hero, ex-cop and reluctant leader Rick Grimes.

As Rick, Andrew Lincoln has his moments – his utter despair in the immediate aftermath of Lori’s death was one of the series’ more wrenching scenes – but ultimately he can’t do much with a role that switches back and forth between two primary modes: one where Rick is the greatest leader in the world (or, at least, the greatest leader available in this corner of the post-zombie world), and another where Rick is tortured, mopey and wants no part of leadership. The question of who is and isn’t a good leader, and who wants to be, is a popular theme in TV drama – “Lost,” a show that’s been an enormous influence on this one, at times seemed concerned with nothing else – but it’s about the least interesting angle on the zombie apocalypse that I can imagine. And the show has gone round and round on the issue so much with boring ol’ Rick that it’s all but impossible to do anything else with him. Even if there was another extended period where he wasn’t in charge, it would be laced with subtext (intentional or not) about the other times he tried to step down from the top post, only to be pulled back in when someone else failed.

And the amount of time devoted to Rick’s tedious, circular struggle winds up making it very hard to service the other characters. There are people who have been on the show for years whose names I still have to be reminded of (Beth, Hershel’s younger daughter, to name one), and others who have been around since the beginning who remain ciphers (I still could not tell you what motivates Glenn beyond basic survival and his love for Maggie). On occasion, a character gets significant development, but often it takes forever – samurai sword-wielding Michonne, one of the most popular figures in the comic, was little more than a scowl and a katana for most of her first TV season – or else the show kills off or otherwise removes that person. Perhaps the most successful bit of character rehab involved Carol, a mousy domestic abuse victim in season 1 and a catatonic grieving mother in season 2 before evolving into one of the show’s more aggressive and morally complex characters over the last year and a half, but Rick sent her into exile just as she was getting really compelling. (Though with the characters all being nomads after the destruction of the prison, it’s entirely possible Carol will return in this season’s second half.)