This time last year, Doctor Who as a series, Steven Moffat as a show runner and Matt Smith as a leading actor all had a lot to prove.

Could little known 20-something Smith summon up sufficient gravitas to portray a Time Lord, or would the memory of David Tennant's powerhouse performances prove too strong for the new generation of fans to accept a new Doctor? By casting Karen Gillen as his assistant, Amy Pond, was Moffat sexing up and dumbing down a British televisual institution?

If casting Smith caused consternation for some, the existential angst that epitomised the final episodes of Tennant's Time Lord had annoyed others who saw needless self-indulgence. And all the questions hanging over the series could be debated at length as Smith's casting was announced so early that the Tenth Doctor was conducting his doom-laden farewell tour beneath the shadow of the hip young gunslinger preparing to fill his Converse shoes.

The rampant success of the show's revival under Russell T Davies's stewardship had erased the memory of the uncertainty over whether audiences would take to a revived, regenerated Doctor Who at all back in 2005. But now it felt as though the backlash was brewing. It was by no means a foregone conclusion that the series would retain its place as the most eagerly anticipated fun-and-fear-for-all-the-family drama on the box.

Though the Moffat-Smith generation has its critics, for many, the concerns vanished within the remarkable opening sequences of their first episode together, as Amy Pond and the Doctor forged a lifelong friendship in the blink of an eye. He had me at "fish custard".

Smith's was to be a Doctor both witty and wise, old and young, his scattergun delivery and inquisitive, professorial air dove-tailing with Steven Moffat's snappy writing and obsessions with fezzes, bow ties and Jammie Dodgers. One of the show's core strengths, the TARDIS, was also – if you have a time machine, use the hell out of it, rather than relying on the boring old sonic screwdriver as a fix all.

Then there were the scares, designed specifically to prey on youngsters' fears. So we had monsters climbing out of the television screen ('Flesh and Stone'), threatening to come through cracks in the bedroom wall ('The Eleventh Hour'), living next door or upstairs ('The Lodger') and the unnerving thought that everything you think is real could be a lie ('Amy's Choice').

"Children rank episodes in terms of scariness – we put the jokes in for the adults," is how Moffat explains his method, his mission.

Hopes, then, are high as the second series featuring the Eleventh Doctor approaches. But there's no doubting that Moffat is taking a risk with two-part opening story 'The Impossible Astronaut' and 'Day of the Moon'.

With Smith fully established, Moffat has dictated that this will be more of an ensemble piece. Amy and Rory Pond (Gillan and Arthur Darvill), and River Song (Alex Kingston), are all heavily involved - they even team up without the Doctor at times, giving the episodes an inclusive feel. Their presence also suggests immediate and present danger, for series finales are usually time to utilise the full team, not an opener.

As dark and intricately plotted as any episodes seen in recent years, the death of a major character (as has been widely trailed), complete with funeral pyre, inside the opening minutes heralds a series that promises to be more intense, more complex and more unsettling than its predecessor.

Sinister new monsters The Silence, who – in a neat twist on the weeping angels that come to life when you blink – fade from memory the moment they are not in view pose a whole new challenge. The feel is eerie, the terror more psychological; a hidden menace that lurks in the shadows.

Stretching the budget to film some of the two-parter in Utah, setting scenes in Richard Nixon's Oval Office, in Area 51, in New York, around the Apollo space program, and having the Doctor interact with US history (as well as Laurel & Hardy), suggest that this is a series now aimed squarely at worldwide – or (BBC) Worldwide, perhaps – domination. Twice in the opening pair of episodes, a character is heard to utter 'Doctor who?' in response to the Time Lord's introduction. An oversight? Poor writing? More of a nod to viewers in the US, who, for the first time, will be able to see the series, in HD, on the same day as the UK transmission.

If the openers are less immediate, despite the fancy settings – albeit with a few trademark Moffat moments – they should ultimately prove more rewarding. Alex Kingston is especially impressive. Scenes in which River Song silently despairs at the thought that, because her regular meetings with the Doctor are happening out of order, they are drifting apart in time even as he visibly, movingly, falls in love with her, are clever, disarming, heartbreaking.

Moffat has also taken steps to avoid one of the pitfalls of a series that depends, to such a large degree, on a believable sense of jeopardy. Mid-series lag, which can make some episodes feel missable, has been side-stepped with the neat trick of splitting the series into two halves – with a summer holiday to recover from the first seven episodes.

With a piratical star turn from Hugh Bonneville, guest appearances from Suranne Jones, Lily Cole, Michael Sheen (well, his voice), an episode called, intriguingly, 'The Doctor's Wife", written by Neil Gaiman, another that Moffat describes as "The Thing meets Made in Dagenham" and a mid-series finale in which we finally learn River Song's secret, this should be all killer and very little filler.

"There are several cliffhangers, a couple are real belters," says Moffat. "[By splitting the series] we get two finales and two first nights. We are absolute tarts."

We are less than two years away from the show's 50th anniversary. As we would expect from a series that continues to cherish its past, this momentous landmark will not pass unheralded. Here's hoping that Smith will still, as he has hinted, be involved, because Mr Moffat is already working on something very special.

"I've got a plan," he grins. "The plan changes a lot, but there definitely is one…"