Well that was an enjoyable if thoroughly unambitious episode.
What I liked:
The Classic Series style of title.
Amy wielding a cutlass.
The Doctor starring across the dimensions.
A return to Horror of Fang Rock, Pyramids of Mars bloodbath style of plotting.
That the Siren was actually trying to help. This reminded me of optimistic tone of the first series.
Hugh Bonnerville was great raising the level of some rather dodgy writing in terms of his characters motivations.
What I didn't like:
Amy shouldn't have been anywhere near as effective a sword-fighter as she was even allowing that the Pirate's didn't want to be cut.
Everyone lived in the end. Would it have been so much to ask that some died as a result of botched attempts to save them
Rory. Dead. Again. What is the point. At this stage Rory has a better life to death ratio than Jesus and Buffy and is only slightly behind The Undertaker.
Interesting to see the online reaction. This seems to be the first episode since The Eleventh Hour where people have realised that the show under Moffatt has plot holes. My feeling on this is very much: Get Over It. The missing deaths of a couple of extra's is not a big deal.
Classic Who often had the problem of padding, not enough story to fit the allotted episodes. This means (arguably) fewer plot holes, but less entertainment. New Who has the opposite problem too little running time for the plots, which tends to result in "holes". As a rule I'll take fast past entertainment any day of the week. Of course, classic Who had stakes of plot holes anyway its just that the fans like to pretend otherwise.
I have had a problem with the Amy/Rory relationship since day one and its finally hit my what it is. I like the Doctor and Amy and I like the Doctor and Rory, but I don't quiet buy Amy and Rory as a married couple. This climax of this episode finally brought home why. There is very little in the way of casual affection between them. Only grand romantic gestures, Amy playing it cool and Rory being protective and insecure. The only exceptions I can think of are parts of Amy's choice and the Pond's at home sequence of The Impossible Astronaut.
Anyway Gaiman's episode is up next so all is cool.