SPOILERS BEHIND THE CUTS
While showing off in a museum by pointing out everything that is mislabeled or just plain wrong to Amy ("It's how you keep score, isn't it?"), The Doctor stumbles across an alien black box with words inscribed on it in the ancient Time Lord language. Figuring out that the message was left by River Song (a companion from The Doctor's future he hadn't met yet, whom first appeared in the Steven Moffat story Silence in The Library and whom knew far more about the Time Lords and The Doctor himself than The Doctor ever thought he'd tell anyone willingly), The Doctor uses the black box recording to track down just where and when River was and get a message of her saying a list of TARDIS coordinates. He arrives just in the nick of time to save her from being lost in space after she blows the airlock of the ship.
Following the crashed ship, The Doctor finds out that River was trying to get his attention because of what was inside the ship - a dormant Weeping Angel (aka the quantum assassin monsters from the Steven Moffat story Blink) - and that she is working for The Church (now a much more militant body than on 21st Century Earth) to destroy the creature. The Doctor, having suffered at the hands of a Weeping Angel before, is all too eager to help despite his own dislike/aversion to River, who is just as eager to flaunt everything she knows that other people don't as he is.
Amy just barely survives an attack by the Weeping Angel, after it is discovered that any image of a Weeping Angel - drawings, photographs, video captures - can become a Weeping Angel. The encounter obviously had some kind of an effect on Amy, who hands sand pouring out of her eyes at one point and later hallucinates that her hand has turned to stone.
Going into the caverns underneath the crashed space-ship, The Doctor and Company find a series of catacombs filled with primitive statues. It is not until he is they are well inside the cavern that The Doctor recalls something disturbing - the inhabitants of this planet were two-headed and yet all the statues they see only have one head. A quick flick of the lights confirms The Doctor's fears - the statues around them are all severely deformed Weeping Angels, made weak and indistinct by centuries without food... and the radiation from the crashed starship has given them power enough to wake up. Trapped between a literal rock and a hard-place, The Doctor asks his companions if they trust him, takes a gun from the leader of The Church soldiers, and shoots out one of the gravity globes in the base of the ship.
* There's just too much going on here. Between an expansion of the lore regarding what little we know about the Weeping Angels, the drama between THIS Doctor and River Song, the subplot regarding just why River is working for the church and why she was in prison at one point in the past, Amy's continued adjustment to the general weirdness around her and the central thrust with The Doctor and company going on a bug-hunt ("Game over, man! Game Over!"), it's a little hard to follow everything even if you know the characters. I can only imagine how confusing this episode must be for any newbies who HAVEN'T seen Series 3 and Series 4.
* Quite honestly, the mysteries and subplots of the supporting cast (River Song's past, what is up with Amy after her encounter with the angel) and what we learn about the Weeping Angels are much more interesting than The Doctor and the main plot.
* The Doctor continues to be an unlikeable dick. More on this later.
THE GOOD PARTS
* The opening scene with River Song IS a glorious spy-epic tribute that plays really well.
* Amy continues to impress, managing to save herself - well, mostly - from the Weeping Angel by pausing the video during a skip in the recording of the Weeping Angel.
* The Weeping Angel coming through the video screen scene is pretty damned effective. Not quite as scary as Blink but it does answer some longed-joked about questions regarding how Weeping Angels reproduce - they just wait for some idiot to come along and do their portrait. :)
WHAT DO I THINK OF THE DOCTOR NOW?
He's not just a dick in general. He's a dick who goes out of his way to push people's buttons.
He seems to hate River - not just because she used him to get out of a tight spot - but because she does seem to be smarter than he is. He goes out of his way to stick it to the Bishop and his men, to the point of acting like a kid poking an anthill with a stick. In fact, he's so obnoxious that I actually cheered at the end when the Weeping Angel (speaking through a simulation of the soldier it just killed) mocks The Doctor for allowing other people to die while he is showing off.
The Final Verdict: The action in the background is more interesting than the main story. That's a problem when you're bringing back the most feared monsters of the current series. As it is, there's just way too much going on to focus on anything what with the return of River Song, the hint of her secret past, the loathing between The Doctor and River AND the return of the Weeping Angels. Even the ending is anti-climactic.