I don't know what was the bigger surprise: the true identity of River Song or the fact that the next episode is called "Let's Kill Hitler".
This is a story that like the TARDIS is simultaneously big and small. When the Doctor takes out a Cyberfleet (full kudos for using the ships from "The Invasion") in the pre-title sequence, you know that you're in for a large story. However, this multi-location epic involves a number of very intimate scenes with Team TARDIS, particularly between Rory and Amy.
Let's start with the multi-locational aspect: the jumping about collecting people bit in the first act is rather reminiscent of "The Pandorica Opens" and works just as well. Mind you, when the Sontaran came up, I ended up thinking of a certain recurring character in the Gallifrey Base Screencaps thread... They're going to have some fun with that...
When we get to Demon's Run, things get even more interesting. There's a lot of "soldiers at work" dialogue that gives what might be one-note characters a lot more foundation and makes you feel sorry for them. Lorna Bucket reminds me of "Lynda-with-a-y" from way back in "Bad Wolf" and touches the audience in a similar manner.
I wasn't too keen on the portrayal of the Clerics. The Moff is an atheist, I'm a thin Anglican. We're not going to agree on much in the religion field, but I honestly felt some of the stuff was overdoing it a little and could have been reined in.
Matt Smith seemed slightly off at times, but made up for it in others. I think I find myself comparing him with Tennant more than I really should and I know the Doctor was supposed to be subdued then, but still... Great stuff from Arthur Darvill as usual and Karen Gillan was also pretty good. Alex Kingston, who doesn't appear all that much, was also wonderful.
The plot was excellent and it was good to see the Silurians again - they're one of the better 'new' creatures of the Moffat era. The dialogue was excellent as usual and I see that the Moff still is doing the gay jokes. Plus I found the idea of the Doctor speaking 'baby' great; there's strong evidence that all babies speak in the same language.
Then that ending: a lot of things make sense as a result, including River Song's name. We still haven't found out who [spoiler] the Doctor in "The Impossible Astronaut", but I guess we'll find out at some point. It's a great point to end for the mid-season break.
9/10. You've got to be something truly special to get a 10 and this wasn't quite it, for a few reasons. Still, one of the best episodes of the season so far.