World War I rages and things are getting grim at that fictional, many-roomed North Yorkshire countryside castle known to us all as Downton Abbey: Dashing distant cousin Matthew, the heir apparent, is doing battle in the trenches of the Somme. At home, the Earl of Grantham, his wife, daughters and their loyal staff bravely agree to let the castle become a rehab hospital for wounded British officers.

For all the stiff upper lips, bad news nevertheless abounds. People are always walking into rooms (those jaw-droppingly fabulous rooms) bearing just-opened letters and telegrams: I have terrible news, they say. Or: Bad news, I’m afraid.

Sorry to say that I must also chime in with a spot of bother: After such breathless anticipation, the second season of “Downton Abbey,” which begins Sunday night on PBS stations, fails in a few important ways to match its original charm. It instead becomes a cautionary example of what happens when we get precisely what we ask for.

The first season, which aired a year ago to runaway praise and viewership, was a wonderfully kinetic juggling act of highbrow drama, historical sweep and character development. It was great fun to watch, not only for anglophiles (an easy get) but also, more surprisingly, for anglophobes. “Downton Abbey” struck an odd chord in an era of 21st-century economic dissonance and disgust. It was and still is the very definition of escapism, dialing back 100 years to celebrate the wealth gap rather than disparage it. It persists in the fantasy that a quaint and even tender co-dependence exists between the haves and the have-nots in their employ. To our lasting humiliation, we gobble it up.

The first season was also only six hours long, which at the time seemed too brief. Viewers got a taste of “Downton Abbey’s” soothing opiate of corseted class stricture and meticulous manners and instantly craved more. Count your TV critic among its swoony fans; just last month I put the series at the top of my list of 2011’s best TV shows.

So what goes awry this time? It’s quite possible that we just wanted it all too badly, a desire most sequels struggle to fulfill. “Downton Abbey” went back into production on a wave of demands: Make it richer, make it longer and give us more, more, more; now, now, now. Writer and creator Julian Fellowes hastily came back with a lot more.

But that’s about all he’s come back with. At 10 sumptuous hours in total length, “Downton Abbey” lacks surprise and is stretched precariously thin, a house full of fascinating people with not nearly enough to do, all caught in a loop of weak storylines that circle round but never fully propel. Built on a recurring theme (and historical generality) that the war will change British life and dismantle its musty social barriers and norms, “Downton Abbey” seems unwilling to fully engage that transformation.

Missing momentum

In the first eight hours (parts 1-6; PBS provided all but the final two-hour episode in time for this review), the characters endure the war with a lot of minor drama but little in the way of profound loss or personal change, even though the script keeps promising full-on disaster. The foreshadowing is often quite thick, but the follow-through is often next to nil.

Midway along, you’ll get the sneaking suspicion that Fellowes adores his characters far too much to let anything of real consequence happen to them. Affairs are pondered but unpursued. A disfigured stranger arrives in comically stagey facial bandages, claiming to be someone the family believes dead, and then disappears as quickly as he came. A member of the staff schemes to commit a crime of protest during the visit of a dignitary, but what happens instead is anticlimactic, to say the least.

Momentum — the first season’s strongest quality — now eludes “Downton Abbey.” As before, no scene ever lasts longer than a few minutes at most, which allows the show to track 20 different characters trying to solve at least 20 different crises. This time, that can often feel like prolonged chaos, and it leaves little room for character development. Everyone just keeps updating one another on the same gossip.

The writing is flat from the first. One by one, the characters return in the opening episode in a way that feels as if they’ll be greeted upon entry by Lenny-and-Squiggy-style applause. Plots unfold clumsily, and relationships are teased out past the point of believability. A few hours in, you’ll become able to say a character’s lines seconds before he or she says them. You’ll no sooner think of a question or historical point (what about the Spanish flu of 1918?) than it is suddenly addressed. And a couple of deathbed scenes would give soap-opera writers a fit of the giggles. It’s as if the United Kingdom has finally returned a gift America gave it years ago: “Knots Landing.”

Speechless beauty

But now that I have the bad news out of the way, let’s focus on the new “Downton Abbey’s” strongest knack: beauty.

Splashed across a high-def screen, the castle and grounds (Newbury’s Highclere, in real life) radiate a breathtaking prettiness. The clothes will leave you speechless — and not just the parade of gowns that Countess Cora (Elizabeth McGovern) and her daughters wear to dinner each evening. At one point, I was transfixed by the lace pattern on the bib of a housemaid’s apron. The fact remains that if “Downton Abbey” showed a series of uneventful days and nights in the lives of these alabaster-skinned people, and concerned itself only with domestic details of meals and housekeeping, many of us would still be hooked.

These are not just mere choices of costume and lighting. To enjoy “Downton Abbey” is to vicariously luxuriate in their luxuriating; to admire the show’s adherence to period specifics. The look and feel of “Downton Abbey” must carry the day now, since the story doesn’t really come along.

Season 2 picks up where things left off. It’s 1916 and the war consumes every thought and worry. Robert Crawley, the Earl of Grantham (Hugh Bonneville), suits up in his military garb each day, frustrated that it’s merely a symbolic gesture, while third cousin Matthew (Dan Stevens) survives the front lines.

Downstairs, Mr. Carson (Jim Carter) and his staff make do with the fact that the war has taken all available footmen off the market. An independence-minded and petulant young maid (Amy Nuttall as Ethel Parks) joins the crew, as does a returning war vet with a bad case of shellshock named Mr. Lang (Cal Macaninch), who takes the place of the Iagoesque footman, Thomas Barrow (Rob James-Collier), the conniving footman who went off to fight the war.

Fear not — Thomas hatches a scheme to get back to Downton, where he and his partner-in-crime Mrs. O’Brien (Siobhan Finneran), resume their acts of spiteful meddling.

Upstairs, much is unchanged. Eldest daughter Mary Crawley (the drab Michelle Dockery) travels back from London, where she has been half-heartedly wooed by a newspaper publisher with aristocratic aspirations. Mary’s still pining away for Matthew after their ruined courtship, a marriage that would have conveniently secured Downton’s future, since none of the earl’s children are male. Everyone in the house, in fact, still rues the day Mary and Matthew split and hope the romance can be rekindled. It’s “Downton Abbey’s” will-they-or-won’t-they hinge upon which the whole world hangs.

Renewing her efforts to that cause, the great Maggie Smith returns as Mary’s grandmother, the dowager countess Violet, “Downton Abbey’s” favorite character. This is another case of Fellowes giving viewers perhaps too much of a good thing; the cutting quips that made Violet so delightful in Season 1 — and, indeed, made her a symbolic bridge between the Victorian age and the progressive future — are tripled and quadrupled here. (“Don’t be defeatist, dear. It’s very middle class.”) Smith revels in every moment of it and her fans will, too.

Early on, upon learning that Mary and Matthew will both be at Downton on the same night for a war-benefit concert (and that Matthew is bringing his new love), Countess Violet gets excited at the dramatic potential, because, she says, she’s not a fan of Greek tragedy, where “everything happens offstage.”

But she could just as well be acknowledging that this iteration of “Downton Abbey” leans too much on telling rather than showing. People talk about what’s happened, what will happen, what might happen — and yet, in almost all the storylines, we never get to see what does happen, especially if it happens outside Downton. The war itself, for example, is depicted through glimpses here and there, with spotty computer-generated vistas.

If it weren’t for the work of Smith and “Downton Abbey’s” other lead players — especially Joanne Froggatt and Brendan Coyle as the star-crossed housemaid and footman, Anna Smith and Mr. Bates — the show would verge on self-parody.

And yet, watching “Downton Abbey” remains a treat worthy of blankets and biscuits and rapt adoration. Its shortcomings merely take away some of the polish. When Armistice Day arrives in November 1918, the grounds of Downton are still swathed in a lush and springlike green, rather than a gray British fall. It’s heartbreaking to notice (and get hung up on) a stray detail like that, to catch “Downton Abbey” doing it on the cheap, but there it is.

Downton Abbey

(two hours) returns Sunday at 9 p.m. on WETA and MPT and continues weekly through Feb. 19.