When Steven Moffat tweeted that this first run of Sherlock peaked with the very last scene, he wasn't just trying to keep watching 'til the end. With snipers, explosives and trigger-fingers this was more devilish than a Spooks cliffhanger - it's as though Moffat and Mark Gatiss were worried that the show wouldn't be recommissioned. And while that seems highly unlikely, a perverse part of me almost doesn't want the show to come back so the ending can be preserved forever.

First though, a little housekeeping. Three stories in and we see the continuity blend together, the series hitting its stride just as it ends. We see Watson's blog beginning to make ripples around London, mirroring his dispatches from the books, and cross-stitching in the series' own mythos. John names his post about the taxi driver caper from episode one, A Study In Pink, the same title of the episode, itself an echo of the first Holmes novel A Study In Scarlet. Sherlock is as unimpressed as he is genuinely baffled that anyone would need to know the basics of the solar system. They're becoming rather cute together.

It was also nice to see Lestrade and Co back. Yes, yes, we can see how it seemed a good idea to replace them with the prickly DI Dimmock last week; taking Sherlock out of his comfort zone and stopping them turning into a Scooby Gang. Thing is, we like them as a Scooby Gang. The perma-befuddled Lestrade; the grumpy ladycop Sally Donovan; Gatiss's lip-licking Holmes-brother Mycroft. Together they give proceedings a heart which Cumberbatch's moody and irascible Holmes can't help but lack on occasion. More of them next series please, not less. And more Mrs Hudson.

And so to this week's episode. As the real engine behind this revival, it falls to Gatiss to tie things up – and it feels like, limited to one episode, Gatiss chose to write several all at once. Any of Moriarty's puzzles in The Great Game could have been fleshed out to an hour. Factor in the missile-plans subplot and it added up to a truly blockbusting conclusion.

It certainly made last week's lurching story The Blind Banker feel like filler. Wiring up citizens to explosives and having them read text messages to Sherlock takes a spectacular brand of cruelty, and each of the crimes the detective had to solve was more ingenious than the last. This could only be the work of a mind equal and opposite to Holmes – any fears the Moriarty reveal would be an anticlimax at this point melted away.

This "consulting criminal" was a brilliantly impish and petulant creation, younger, more Irish than expected, walking the same tightrope of madness/genius as, say, John Simm's Master. Moriarty's incredulous retort to Sherlock pointing out that people have died – "that's what people DO!" – was delicious.

The more deductive among you might have called him earlier on "playing gay" in the hospital, because a)why would a gay man want Molly as a beard, and b)his name was Jim (and Moriarty was always called James). I didn't see it. But what a magnificent villain, with an arc that could have stretched over 10 episodes. It's a shame we probably can't have him back.

So with the series over before it's even started, how did we feel about Sherlock? Did the modern-day setting work? Did we like the 90-minute format? What other classic Holmes elements should they bring back next year? And did anyone else notice how the main visual influence on the show appeared to be the video game Heavy Rain for PS3?