The cliffhanger resolves awesomely, as the Doctor uses the crashed ship's gravity controls to flip the world around the Angels and get everybody onboard. After a lot of running around and yelling, everybody ends up in the ship's oxygen forest, where Father Octavian finally tells the Doctor that River Song is a prisoner and murderer. Amid much play with gravity wells and increasingly dubious explanations regarding the Angel in her eye, Amy spends the first half of the episode counting down from ten without knowing it, and the second half wandering around the forest with her eyes closed, subject to greater and greater -- and more ridiculous -- made-up rules she has to follow: "Walk like you can see, but don't open your eyes" is, I would say, taking the "let's pretend the floor is lava" situation with this show to a whole new level of stupid.
Speaking of the Vashta Nerada, if you enjoyed the Library you'll probably love this one, considering it's almost exactly the same story, albeit with better appurtenances and design (if worse effects -- good Lord the CGI on that first gravity-reversal). It's certainly as much of a poorly paced letdown, storywise, as the two halves of the Library story worked out to be. The forest itself is pretty cool -- until the "treeborg" technology is revealed to be a low-budget version of Pandora from that classic piece of cinema Avatar -- and the Angels are still pretty fun -- until we actually see them move, which invalidates the entire postmodern point of "Blink" without adding anything positive to the story -- but never really getting a handle on emotionally inorganic things (why the Doctor spends most of the episode screaming his ass off at River), or why every five seconds we get hit with another impossible fucking task that gets accomplished so the music can swell and everybody can gaze adoringly at everybody else, those things are getting old.
In the end, we finally discuss the Crack and Amy's failing memory, as the majority of both the priests and the Angels end up getting fed to it. Seems an "explosion" of some sort, temporally located on Amy's wedding day, has caused the Crack, which is busily rewriting people out of history and chasing her across time. Which is exactly as paint-by-numbers a seasonal arc as we expected, but still kind of annoying to see play out, even as River drops a joke about the Pandorica (doesn't mention Silence, though) before promising we'll see her again, shortly.
...Which would be a fine ending, making this a B- follow-up to last week, except for how Amy then decides the perfect coda would be to take the Doctor back to her creepy house on her wedding night, and out of nowhere try to fuck him. So the Doctor gets to act skeeved out, and Amy gets to chase him around in heat with her dress up over her head like some kind of sex abuse victim on Law & Order, and that's how we learn the key to saving the universe is getting Amy's slutty ass married... Before it's too late!
Luckily the Doctor did not blow up the Byzantium last week: He blew up the gravity globe, which sent gravity spilling everywhere, so when they jumped up they actually jumped down, and now they are upside down, the enemy's gate is down, and they are dancing on the ceiling. Let's talk about it for a long, long time. River gets it, army guys never get anything and also in this case are big shitty fake CGI, Amy for some reason doesn't get it -- "Doctor, what am I looking at? Explain!" which earns her a literal "Oh, come on. Amy, think!" -- and then acts dipshitty some more as he tries to usher them all into a corridor which has its own fake gravity, perpendicular to their current upside down gravity. The whole cast pitches in at this point to explain to Amy what should be immediately apparent, not to mention it doesn't really matter if Amy understands the finer -- or I mean, totally obvious -- qualities of artificial gravity, because those Angels down there are looking more and more like actual Angels all the time.
But really it's because A) We don't trust the audience to understand things, even though we really should and B) We see no problem using Amy as a stand-in for the hypothetical audience's hypothetical retardedness, which is a separate issue but also an obnoxious problem. When you're shoving every single idea you've had into every single episode, and somebody says it's confusing enough that you have to treat one or more characters like they've had a head injury... Well, you get this episode. Which is a rollicking adventure, or rather a serial set of meaningless mini-games, that lasts for an hour and signifies nothing. Which is still more fun than watching River and Donna swan about in the gauzy Lady Fantasy of the Library for an hour, I'll grant you, but is just as much of a letdown coming off the first half. But whereas earlier irritating episodes were impossible to summarize, this one is fairly easy, because nothing actually happens.
The Angels or something closes the team -- River, Doctor, Amy, Octavian, a soldier -- in the immediate corridor, open the outside door, and then come closer, closer, closer. If you still think they're scary, I guess they're scary. The lights start going off and on, the gravity might fail, it's all hugely important. So ramped up is the scale and scope at this point that it actually becomes self-parody: "There's no way to override [whatever]! It's impossible!" River says, and the Doctor says, "How impossible?" and River says, "Two minutes." Which is like everything embarrassing about Moffat happening at once.