The Gallaghers aren't easy to love. In five previous seasons of Showtime's dramedy "Shameless" (which returns for a sixth on Sunday night), viewers have seen the members of this wild South Side Chicago family struggle with a poverty that affects both the pocket and the soul. Good at heart and bad to the bone, every character on the show will lie, cheat, steal, fornicate and worse, with a voracious appetite for self-preservation.

The empathetic texture with which all of this is portrayed, however, has always been "Shameless's" core attribute. Human despicableness informs so many of our favorite shows, to the degree that we become largely inured to the moral shortcomings of antiheroes. "Shameless" works at a depth and shape that are surprising in a show where the primary aim is shock value.

Adapted from a British series in 2011 by American showrunner John Wells (of "ER" and more), "Shameless" has soared and wallowed; in keeping with the bad luck that plagues its characters, it usually goes underpraised and underappreciated in this crowded era of good TV.

Sunday's episode (9 p.m. on Showtime) opens with the Gallaghers more or less where we left them - and also with a distinct feeling that the show might be running out of gas. Frank Gallagher, the incorrigible paterfamilias played with booze-breath brio by William H. Macy, is in a state of pathetic grief over the loss of Bianca (Bojana Novakovic), a terminally ill doctor who accepted Frank's offer of last-minute reckless abandon, blowing her savings on crack highs and running off with him to a Costa Rica beach.

Bianca was everything Frank ever dreamed of - wealthy enough to supply his insatiable habits and tolerant of his self-absorption. While he slept, she walked off into the sea. Now Frank spends most of his time on the grass at Bianca's grave back in Chicago - humping it, even, in autoerotic tribute, until a groundskeeper chases him off with a water hose.

Macy's over-the-top performance is often touted as the main attraction of "Shameless," but any viewer of the show recognizes its centrifugal force comes from Emmy Rossum's superb turn as Fiona, the eldest of the Gallagher brood, who, as a teenager, took over the parental reins from her alcoholic father and absentee, bipolar mother. Fiona brings an ethically flawed yet resourceful order to the household chaos. As "Shameless" has progressed (and its characters' lives devolved), the other five Gallagher children have escaped Fiona's control - all but Liam, the mixed-race youngest half-brother who, as a toddler, got into Fiona's stash of cocaine.

Yes, indeed - this is a show where a baby finding cocaine is par for the course. ("Shameless" is not entirely devoid of consequence; Fiona went to jail for that.) Any show nowadays can come up with ways to disturb or sicken us or yank the easy chain of prurience - and many do. This season I'm struck by three topical themes on which "Shameless" has consistently and uniquely delivered:

1. Poverty - from a white perspective. In translating a British show about an on-the-dole family in Manchester to a story about a struggling family in the reputedly territorial Canaryville neighborhood on Chicago's South Side, Wells and company have said they resisted suggestions to set the show in a trailer park somewhere in the Southern U.S. sticks. That is too often American TV's answer to what white poverty must look like, rife with yokel cliches.

On "Shameless," viewers are fully immersed in the urban details of the Gallagher family's plight - as well as that of their neighbors. Here and there, viewers have seen the ways Fiona navigates what's left of the nation's public assistance programs (and the futility therein); Frank, known to every emergency room in town, somehow managed to get a liver transplant without insurance. ("God only gave me two livers," he reminds an acquaintance in a new episode, limiting himself to six ounces of beer a day.) With just enough realism to counterbalance the show's more outlandish developments, "Shameless" always makes sure to provide enough detail on how the Gallaghers stay fed and sheltered.

Jobs come and go. Cash is king. We've accompanied the family to health clinics, family court and detention centers and seen how a few hundred dollars might have made all the difference.

The Gallaghers and their neighbors carry a particular grudge for the upper class - a resentment that has nearly derailed eldest brother Lip (Jeremy Allen White) in his quest to remain in good standing at the University of Chicago. It also, in a way, cost Fiona the only upwardly mobile office job (with health-care benefits) she ever had. The characters on "Shameless" resent the gentrification (and accompanying hipster-fication) in the neighborhood. Although this is milked for its comic value, there is a fierce pride that informs it, a rejection of the yuppie values and lifestyles that still inform most premium-cable shows.

2. Embracing the innate criminal impulse. As a chronic goody-goody, I find in "Shameless" an almost cathartic disregard for rules, manners and the law. This is not the same as watching serious dramas about mobsters or drug kingpins. The Gallaghers find their identity through a genetic predisposition for dishonesty - it's the family talent. They cut corners, cheat and game whatever systems stand in the way of their survival.

The real trick here is how "Shameless" can endear the Gallaghers to the viewer, even when the family is at its most reprobate. Aspiring to be the shadiest Gallagher of all, 14-year-old Carl (Ethan Cutkosky) emerges this season from a juvenile detention center sporting cornrow braids and enjoying the wide respect of a network of black drug dealers; his family celebrates his return with a bargain grocery-store cake frosted to celebrate some girl's quinceanera.

It's an image that is at once absurd, tender and vaguely terrifying as we realize Carl is past the point of no return. In the way, it accepts criminals for what they are, without saddling them with deep meaning or artistic metaphor, "Shameless" really has one peer, in the work of Jenji Kohan's "Orange Is the New Black" (and, earlier, "Weeds").

3. Sex as a means to personal freedom. Some of the best recent work on "Shameless" can be seen in Emma Kenney's heartbreaking and intelligent portrayal of the youngest sister, Debbie, who is now 15.

When the show began, Debbie was an innocent girl who believed her family's troubles and idiosyncracies could be surmounted with enough optimism and ingenuity. Growing up in a house swirling in sexual antics - which included Fiona's successive boyfriends; Frank's improbable conquests; Lip's legion of girlfriends; brother Ian's (Cameron Monaghan) coming out and eventual pairing with the neighborhood bully, Mickey Milkovich (Noel Fisher); the uninhibited and steamy dramas from neighbors Kevin and Veronica (Steve Howey and Shanola Hampton) - Debbie was certain to eventually crash into her own awakening.

Suffice it to say, sex hasn't made Debbie any happier or more secure, but it has challenged the show's writers to come up with some impressively frank scenes that get at the awkwardness and constant ache in a teenage girl's emotional life. It's easy to see why a girl like Debbie would view pregnancy as an upgrade. Fiona's discovery that Debbie has become sexually active leads to an immediate trip to the local Planned Parenthood clinic.

In the same way that "Shameless" distinguishes itself portraying poverty and criminality, it also can be seen as remarkably sex-positive. True, in 60-plus episodes, it has featured many shocking scenes of perverse predilections, inappropriate liaisons and degrading outcomes.

Yet through such filth, a viewer sees that each of its characters has found that sex can sometimes be a clear path to personal freedom. Sex is the one thing that the Gallaghers can own free and clear. "Shameless" is noisy about everything, but its loudest and surest moments rejoice in pleasure.