Why wasn't there a whole episode built around this scene?

I've thought long and hard about this one. For obvious reasons - which will be gone into in immensely spoilery fashion below - I was a gibbering wreck at the end of this episode, as Russell T Davies finally made happen the thing that just about every Doctor Who fan in their right mind has wanted to happen for about forty years. My immediate instinct was that this was an utterly incredible episode, and that it was easily deserving of the first five-star review that NTS has given out for the second series.

And then I stopped for a moment. Was I just being blinded by those staggeringly good - and almost unbearably tense - last ten minutes? Were they a cunning act of smoke and mirrors, to mask a disappointing episode - nay, a disappointing series? Certainly, this episode's counterpart last year, Bad Wolf, benefited from a similarly wonderful closing act, leading to fonder reactions than such an admittedly good, but not brilliant, episode would have otherwise garnered. So I thought for a bit about everything that had happened in the preceding thirty-five minutes or so. And then I watched the episode again. And I thought, fuck it. This was brilliant. As an all-round piece of TV, I'm not sure it quite matched up to The Girl In The Fireplace as the best of series two, but as an insanely gripping piece of dramatic sci-fi guff, it was about as good as it gets.

God knows this second series has flattered to deceive at times, but this episode was a classic example of hitting almost every single note absolutely dead-on, right from the word go. For starters, how about that pre-credits sequence? For me, that was the best opening lead-in in twenty-six episodes so far - with a shiver-inducing flashback to Eccleston, an incredibly ominous but perfectly-judged voiceover from Rose, and - to boot - a breathtaking shot of a beautiful alien landscape (with what appeared to be giant underwater creatures, swimming in the air) that simply made you wonder why we didn't get a whole episode set there instead of, say, New Earth.

The first act of the episode was then littered with comedic moments that, by and large, worked pretty well. Glossing quickly over the Ghostbusters bit - I didn't hate it the way some did, but it could have done without the music - the "channel hopping" sequence was an absolute joy. As series two has gone on, the light-heartedness has annoyed many, but it's clear that it's been building to a sense of overconfidence that will surely come to have serious repercussions; and in this instance, it was clearly going to be the last such segment before things really kicked off. As it was, anyway, the Eastenders bit was bloody hilarious - far, far funnier than it had any right to be, in fact.

Once the action shifted to Torchwood, it was the old rather than the new elements that proved to be most effective - although Tracy-Ann Oberman played the calculating, "I'm in control" uber-bitch with clear relish - with the return of Mickey and the growing menace of the Cybermen the real highlights. In the case of the former, it's sure indication of how far he's come since being the annoying twonk who got eaten by a wheelie bin in Rose that his return was such a joyous and significant moment. No-one could say they didn't predict it, but the quick reveal and "Sssh!" gesture were neatly handled. Mickey has shown real growth as the series has gone on - arguably more than Rose has - and his metamorphosis into an Ace Rimmer-style heroic version of his previously cowardly self somehow hasn't felt awkward at all.

As for the Cybermen, they were everything that they should be - and everything that they weren't in their earlier, underwhelming two-parter. I commented around the time of Rise... that we could have done with plenty more sequences of Cybermen invading ordinary streets and overwhelming ordinary folk, and we got them by the bucketload here (with more resonance, too, since they were now in "our" world). The moment where one Cyb burst through a suburban front door, only for the fleeing family to be confronted by another at the top of the stairs, is destined to go down as an all-time classic "That bit gave me nightmares as a kid!" moment for future generations. The reference to Tomb of the Cybermen, meanwhile, as the metal monsters ripped through plastic sheets, was a welcome yet subtly-done touch. I can't have been alone in figuring out the true nature of the ghosts - from the Doctor's "a footprint doesn't look like a boot" to the evidence of handlebars atop the shadowy heads - but given later revelations, this didn't feel like it was something that necessarily needed to be a huge surprise.

For the final fifteen minutes or so, the tension just didn't let up for a second. With the Cybermen on full-on terrifying form, the stage was set for yet another classic "How will they get out of this one?" invasion sequence (with even the Doctor, for apparently the first time, taking an utterly defeatist attitude). But there was, of course, one final sting in the tail. Personally, I wasn't sure if I ever believed the rumours that the Daleks might show up in the finale - even that gun effect last week seemed like the ultimate red herring. And indeed, with the growing Cyber-menace, it became easy to simply forget about what might be in the sphere, or at least simply assume it was the great Cyber-weapon. Until it became apparent that whatever was in there had to trump everything we'd seen before. And there's only one thing that can one-up the Cybermen. Still, though, I couldn't quite bring myself to believe it until that familiar sound-effect and shape began to emerge... and it's at that point that words simply can't do justice to the swell of emotion felt. Truly, this will go down as one of the all-time great episode endings, one of the finest ever cliffhangers - not just in the history of Doctor Who, but in the history of television itself. I feel for those who had it spoiled beforehand, I really do. Special kudos must also go to the often-lambasted Murray Gold, incidentally, for spending the second half of the episode turning in, for my money, the best piece of score that either series has seen to date. The building menace of the pounding Cybermen theme helped to ratchet up the tension still further, and the segue into the choral Dalek theme from last year at the crucial revelatory moment was spot on.

The best ending in the history of ever. Ever.

Quibbles, then? Well, not everything was perfect. I was a little perplexed by how small and cloying the main Torchwood office was, particularly given the over-the-top nature of Yvonne's character. It felt like a small set without much beyond it. In addition, after how great she was in Love & Monsters, it was disappointing to see Camille Coduri veering back towards "annoying Jackie" mode. But these were minor issues, minor enough that I didn't feel they detracted from my enjoyment of an immensely good adventure.

And then, of course, there was the "next time" trailer. Usually, such a thing shouldn't be worthy of discussion in an episode review, but damned if it didn't leave us enough to discuss! What's in the "genesis ark" (I'd say it couldn't possibly be Davros, but after this, what can you take for granted?) What is going to happen to Rose? And what's this talk of an "alliance"? Since when have the Daleks ever bothered allying themselves with "inferior" races? This is, surely, something that no officially-sanctioned Who story ("canon" or otherwise) has ever done before - Daleks. Versus. Cybermen. We may only be getting a handful of Daleks, and a battle in a single building (rather than the millions, and the war in space, of last year), but this could still be the finale to trump all finales. A promise worth the price of admission alone, irrespective of whether or not it came after forty-five minutes of bliss. Which, happily, it did.