Good Doctor Who monsters have to come back - it's a rule. But my feeling is that you always have to bring back a monster and do something different with it. So although Blink was a very popular episode, it was also a very spooky, cerebral episode.
Last time, the implication was that they were hiding out on earth, as scavengers who are just surviving - they didn't have a big terrible plan. This time there really is a big terrible plan which goes beyond mere survival, and is almost like a war.
The best way to explain the difference between Blink and these two episodes would be to say that I think the best conceived movie sequel ever was Aliens following Alien. It took the same monster into an entirely different type of film.
That is very roughly the model for this. Blink was a small, low-key one and this is the highly coloured, loud, action-movie one.
Filming this scene (above) was a completely surreal experience. I'm used to the fact that in television the first day of filming will probably be something fairly inconsequential and involve a minor character getting shot, or a close up of a hand or something. It's not usually something big and iconic.
So it couldn't have been more iconic - the Tardis was there! It was also perfect paparazzi fodder because it had everything you could possibly have, which wasn't intentional actually.
I vividly remember arriving on that beach. I saw the Tardis in the distance, which was very much the culmination of all that time waiting to get started - which you could argue was two and a half years, or 40 years for me.
First walking onto a big, grand, typical Doctor Who location and seeing the bright blue box waiting was so odd for me. We'd be so careful up to that point, and not put the Doctor Who name on any of our signs but still the paparazzi and fans found us within about 20 minutes!
I was stood on set with my phone, looking at pictures of myself which fans had taken already on the web. On one occasion I saw a photograph of myself watching the filming, which had been uploaded so quickly that I hadn't moved from the position I was in by the time it was on the web!
My other memory is of this day ending early because the tide came in unexpectedly. I did slightly wonder if this would be the shape of things to come.
That scene on the beach was about three pages longer originally. The rain on the second day of filming was so torrential that I suggested I could cut three pages, provided I could relocate them in a new Tardis scene.
I ended up adding the scene which sits immediately after the credits, with River flying the Tardis better than The Doctor. That's a lovely scene, and a much better start to the show, but it's all a consequence of torrential rain and the tide coming in.
On the second day I ended up sat in the production van, very grumpy, hastily rewriting scenes. The story of those two days is really about the plunge from the extraordinary romantic beginning with the Tardis and the big iconic scene, to the reality of actually trying to film it. It was a great lesson in having to cut pages and deal with the reality of the challenges we face.
Later on in the episode there's a really nice accidental moment where The Doctor hangs from the strap on the ceiling and it breaks. The very first time Matt did it, it was an accident - he wasn't supposed to do that, it's just typical Matt, breaking everything - but the director liked it, so he kept it in.
The version we see on screen isn't the real accident, it's him doing it on purpose, but I do think it is very funny. I think particularly the looks from the girls and the fact that he doesn't mention it at all - he just tries to carry it off as a sort of Stan Laurel moment. It's extremely charming.
I think the thing that has come back with Matt is the idea that The Doctor is a bit silly at times. He's a slightly silly old buffer in a few ways.
We find out he's a bit rubbish at flying the Tardis and he trips over his feet and breaks things. Both Chris and David were quite cool Doctors, and while Matt certainly isn't short on cool, he has an amazing clumsiness. He's halfway between Indiana Jones and Stan Laurel.
The Doctor has a belief that he is cooler than he actually is. For instance in that first episode where he yells "Who da man?" and everybody cringes.
It's those moments that really show where the old man comes through in Matt's performance, because there is nothing wrong with a young man shouting that, the awkwardness is when your dad tries to say it. That's The Doctor through and through.
Steven Moffat is executive producer and lead writer for Doctor Who. The Time Of The Angels can be viewed on iPlayer. Part two of the story - Flesh and Stone - will be broadcast on BBC One at 6.25pm on Saturday, 1 May