Some aspects of this episode were quite familiar, e.g. Encounter at Farpoint (the first TNG episode) had an alien creature that was enslaved to power a starbase, and the Discworld novels have a giant turtle carrying a world through space. However, there were enough differences to keep this interesting.
When the Doctor put a glass of water on the ground, he had some funny lines, and I was quite happy to take them at face value; this followed on from the "bonkers" aspect of last week, where he'd do something and then deny all knowledge of it. That then made it more effective when it turned out that he had a sensible reason for it.
When the Doctor and Amy went down the pipe, I immediately thought of Star Wars (episode IV). That seemed fairly straightforward: they were in a waste disposal area, and there was a beastie moving around in there as well. So, when the Doctor gave his little speech, saying "Brace yourself for a shock", I wasn't expecting any great revelation, and I was surprised when he revealed that they were actually inside the creature's mouth. It also made me laugh when he said "I'd love to see the stomach ... but not right now!"
Regarding the lady in the cloak, there were three significant clues to her identity:
1) She said that she hadn't voted because she wasn't technically a subject.
2) The little girl recognised her when she took off her mask.
3) She gave her name as "Liz10".
When she was revealed as Queen Elizabeth X, that all made sense, but my theories had gone off in a completely different direction. It's quite common in SF (or on YouTube) for people to have numbers inside their names, e.g. the Quaddies in Bujold's novels, and I thought that she wasn't a subject because she was somehow "living off the grid". Again, it's satisfying when the story can surprise me without cheating.
I still prefer the old theme tune, but I do like the orchestral music that they've got inside the episodes. That goes particularly for the triumphant music that they played last week during the montage of previous Doctors.
My only real complaint is that the ending seemed a bit heavy handed, because they basically explained it three times: once in Amy's flashbacks, once when she explained it to the Queen, and once when she explained it to the Doctor inside the TARDIS. However, I was talking to someone yesterday about last week's episode, and he didn't understand why the Doctor had gone forward 12 years or why Amy handcuffed him to the radiator. So, in order to appeal to a wider audience it's probably prudent to spell things out every so often.
By the way, I've just realised something about last week's episode: at the start, we see the TARDIS fly past the Millennium Dome and the London Eye, which were built in 1999. So, if Amy's wedding day is 14 years later, that means that she's actually from a few years in our future.
I didn't watch the preview for next week's episode, but based on the general preview from last week it does look good, so I'm definitely looking forward to that.