If there’s one show on television that makes expert critics of us all, it would be NBC’s “Saturday Night Live.” We’ve had so much practice — coming up on four decades — that it’s almost as if “SNL” exists mainly so viewers can dump on it.

Along the way, it has been “SNL’s” good fortune and bad luck to become an American institution saddled with obligations. I happen to enjoy “SNL” in a slump season because it feels like possibility; other viewers beat up on “SNL” for failing their expectations, which are surprisingly deep and complicated, given that it’s a comedy show.

We demand much — sometimes too much, I think — from “SNL.” A happy example would be how Facebook users demanded that Betty White host the show in 2010 and how executive producer-for-life Lorne Michaels gamely granted this wish.

But lately “SNL” has been faced with a more serious shortcoming, which also required public demand and swift remedy: Far too many seasons went by without a black woman in the cast, to the point where even the most dense viewer could notice the lack of diversity and missed opportunities for topical humor. Thus, auditions have been held and an as-yet-unnamed black woman reportedly will join the show in January, where she can participate in sketches that could elevate and illuminate the satire without playing down to stereotype or merely checking off a box. (Cross your fingers, girl.)

Although we occasionally want “SNL” to reflect life back to us, most viewers still just want it to be funny. Or funny again, as some swear it used to be: Criticizing “SNL” almost always centers on a belief that the show was better two seasons ago, or four seasons ago, or back in 2004, in 1993, in 1987, and, most of all, in the mid- to late 1970s. It helps to have lived just long enough to remember for certain that “SNL” has never been fully brilliant in any year.

As proof, I predict the comments field below the online version of this review will soon fill up with complaints that “SNL” hasn’t been funny for (insert number of years here, often in direct proportion to when the commenter was in college) or that, in fact, it was never, ever funny. (For fun, I insist you read the online comments, as well as my review, in the voice of current cast member Taran Killam’s recently added “Weekend Update” character Jebidiah Atkinson, a mean-spirited 19th-century “speech critic” who ripped into Lincoln’s Gettysburg Address: “Four snores and seven yawns ago,” he sneered. “Let’s be honest, Abe, you dropped a real Lincoln log.”)

“Saturday Night Live” was always a talent show and a train wreck at the same time, and even now, in one of its dreaded “rebuilding years” with a raft of new and newish cast members and featured players and a departing head writer (Seth Meyers, 39, off to host NBC’s “Late Night”), “SNL” manages to be funny — sometimes by luck, but just as often through skill.

The show is in many ways immune to criticisms about its wavering quality from era to era, mostly because its legend is built upon the art of improv, which understands that brilliance can be found in the pretty-good-try. The only way to truly enjoy “SNL” (in good years and bad) is to watch from a place of both habit and forgiving optimism; otherwise, all you’ll ever see — particularly this season so far — are the show’s consistent flaws.

These include innumerable sketches that peter out five seconds after they begin — a problem “SNL” has always grappled with, but is worse now. It’s also painful to watch attempts to launch new recurring characters in the void left by the recent departures of Bill Hader, Fred Armisen and Kristen Wiig.

It’s also tempting to resent the show’s sentimental habit of bringing “SNL” alums back for guest spots, as with Tina Fey hosting this season’s opener in September; or when Wiig showed up two weeks ago to reprise her magnificently goony “Dooneese” character as an oddball von Trapp child in a “Sound of Music Live!” spoof.

In one way you’re relieved to see them back; in another way it signals that the cycle is basically inert — as will probably be the case this Saturday, when alum and “Tonight Show” host-to-be Jimmy Fallon hosts with his overexposed buddy Justin Timberlake as musical guest. “Saturday Night Live” spends far too much of its time now being self-referential and nostalgic; sometimes it seems the only audience the cast members are playing to is themselves.

“SNL” simply has too many friends asking for too many favors — evidenced by an endless stream of celebrity cameos that mainly serve to promote films starring alums or longtime friends of the show. When it’s like that, “SNL” reminds me of being part of a captive audience in a high school pep assembly, watching the popular kids act out their lame sketches.

In a weakened state, it’s also easier to notice “SNL’s” puzzling dependence on old premises, such as lampooning talk shows of the sort that no longer exist or only ever existed on “SNL” (“Girlfriends Talk Show”; “Lady Gaga’s [talk] Show”); or making very old hay out of the game-show genre (“New Cast Member or Arcade Fire?”; “Cartoon Catchphrase”). These set-ups no longer apply to “Saturday Night Live’s” original mission, which is to lampoon contemporary culture.

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Yet, despite the slump, “SNL” still offers the security of ritual — something of real value in a pop-culture era that worships disruption and upheaval. The show’s format is as inviolable as the Mass liturgy. (Mass, that is, if more than half the priests were Jewish.) It starts with the “cold open,” where “SNL” displays both its desire and its flailing inability to deliver relevant political satire, followed by monologue, sketches, a song, “Weekend Update,” more sketches, another song, and then, most delightfully, the back end of the show, which is an experimental playground for anyone still awake.

What “SNL” has going for it — what it’s always had and remarkably retains — is its confidence in and surrender to youth, even though it is controlled by a 69-year-old man. Among the new (or relatively new) performers remains a sense of lark and pleasure in partaking in the show’s vaunted traditions. The women in the cast, especially, are harnessing a long-overdue interest in post-feminist comedy; they are beneficiaries of the work Fey, Wiig, Amy Poehler and Maya Rudolph (among others) did in the 2000s.

Kate McKinnon, 29, who came on as a featured player in 2012, proves her versatility in each episode, whether she’s playing a celebrity or a teacher or a politician (Kathleen Sebelius; Angela Merkel) or a dour foreigner (impoverished babushkas; Angela Merkel). She also excels at surreal, uncategorizable characters like Sheila Sovage, a barfly who throws herself at the last remaining customer at closing time.

The same praise applies to the superlative Vanessa Bayer, 32, who joined in 2010 and now finds herself capably shouldering sketches all through the show, the way Wiig used to, whether she’s playing Miley Cyrus or her greatest contribution to date, Jacob the Bar Mitzvah Boy, who comes onto “Weekend Update” and painfully, nervously sticks to a prepared text filled with Borscht Belt attempts to make his grown-up relatives laugh.

Cecily Strong, 29, will take over as “Weekend Update” anchor in January when Meyers departs; her co-anchoring this fall still feels a little flat and comes at a terrible price: So that she could play anchor, we’ve lost her best character, an “Update” commentator called the Girl You Wish You Hadn’t Started a Conversation With at a Party. (It’s a tragesty, Seth.)

The men are on less sturdy footing. Jay Pharoah, 26, patiently outlasted “SNL’s” ineptitude at utilizing its minority performers and now does a passable President Obama and a manically funny take on ESPN commentator Shannon Sharpe, among other characters. Killam, 31, can do anything, which means he has to do everything; it’s exhausting to watch him try to be Hader, Armisen and even Jason Sudeikis all at once. Bobby Moynihan, 36, is similarly good at filling gaps, but his characters — “Update” commentator Drunk Uncle among them — run too quickly into the ground. Kenan Thompson, who is only 35 but has been on the show for a decade, seems at long last bored with his own work — a feeling conveyed to the viewer.

And though “SNL” was dinged for adding too many young white guys to its supporting cast this season (five of them), they’ve shown themselves to be funny and not entirely indistinguishable from one another if you pay attention, especially 29-year-old Beck Bennett (known to TV watchers as the stern businessman in the AT&T commercial who sits at a table and talks to kindergartners about cell phone coverage), who was very funny a couple of weeks ago as a chief executive who behaves like an 11-month-old baby.

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Though their hearts (and theatrical training) belong to the live stage, today’s “SNL” performers tend to succeed most in the pre-recorded bits. Short film has been with the show since its earliest days (think Walter Williams’s “The Mr. Bill Show” all the way up through Robert Smigel’s dangerously funny and still missed “TV Funhouse” cartoon clips). The form took a huge and relevant leap forward when Andy Samberg and his collaborators delivered “SNL Digital Shorts,” and brought the show much-needed juice as a source of Internet fodder.

The millennial members of this cast and writing staff seem most naturally drawn to this genre, whether it’s in sustaining “SNL’s” tradition of pre-filmed commercial spoofs (“Autumn’s Eve pumpkin spice” feminine hygiene products; or a brutally spot-on fake ad for those tacky H&M clothing stores) or in weirder, one-off films. Bennett and another new featured player, Kyle Mooney, 29, seem most at home in this format, especially in a recent film in which two fraternity members explain their elaborate rules for beer pong.

When you rewatch the first half of this current season (as I just did), the new style of humor seems plain as day: Eventually, it’s no longer going to be about over-the-top characters played again and again and again, the last of which may have gone away with Gen X-ers Wiig and Hader and Armisen — Dooneese the malformed sibling; Stefon the strung-out gay clubster; Garth and Kat, the singers who make up their songs as they go.

What the new crop is very good at is playing awkward and comically pathetic people. They specialize in subtle, satirical portraiture (Jacob the Bar Mitzvah Boy; Girl You Wish You Hadn’t Started a Conversation With at a Party) that is more easily recognizable in the present era, in which any real-life situation can be turned into the day’s most unbelievable YouTube video courtesy of a witness and an iPhone. This is where today’s comedy is headed — not in celeb impressions and riffs off political news, but in smartly observed renditions of everyday people. I like “Saturday Night Live” best when it follows those instincts.

Where I don’t like the show anymore is when it is self-consciously meta, essentially becoming an episode of “Saturday Night Live” that is about doing an episode of “Saturday Night Live.”

Going meta is a bad habit, not just in “Saturday Night Live” but in nearly all forms of television now. Going meta is a way of girding yourself for the critics by pre-anticipating their complaints. When the show brought “Scandal” star Kerry Washington in as host last month, amid the growing shamefest about the lack of black women on “SNL’s” roster, the chief artistic theme was going meta: We’ll make fun of ourselves as a way of neutering an important and even institutional shortcoming. (The fact that Washington more or less aced the show was seen, by Monday morning, as a cultural victory and a proved point.)

But going meta is not just “SNL’s” crutch, it’s everyone’s crutch. I went meta near the top of this article — pre-swatting my critics before they even landed on my stinking pile. This is what it’s like to create anything in the digital age: You must apologize for your mediocrity in real time. As a result, we collectively regard the fourth wall the way prospective home buyers on HGTV treat the wall between dining rooms and kitchens — we tear that mother down completely.

“Saturday Night Live” needs to do one last sketch about this — meta about meta about meta — and then get on with the necessary business of being “Saturday Night Live.”

Saturday Night Live

(90 minutes) hosted by Jimmy Fallon with musical guest Justin Timberlake, Saturday at 11:30 p.m. on NBC.