It's sad when a two part story can be summed up with the single word "yawn"
I'm not sure what it is that makes me so apathetic towards this story. It's not actually "bad" as such, I think it's more that it's a half-arsed effort on pretty much every possible level. The script, re-introducing the Silurians, is a rehash of... well... The Silurians (which is not good as it had already been rehashed as The Sea Devils) with a few bits of Inferno thrown in and a touch of The Daemons. The effects aren't the cheapest but the CGI explosion at the end looks rather lacklustre and whilst the large scale shots of the city try their best to look impressive, the running around the tunnels sections look as though the tunnels are made from polystyrene. The regulars aren't particularly sparkling, Smith's not quite at his flattest here but he's completely lacking eloquence and the scenes where he's supposedly being all authoritative leave me thinking "well, I wouldn't be doing what you asked me". Thankfully Amy's absent for a lot of the story leaving us left with a very underwhelming guest cast of two scientists, a kid and his tedious parents. And given that they're allegedly heading for Rio at the start of the story, Amy and Rory look very VERY overdressed.
The first part also presents us with yet another impossibly short time scale. They've got twelve minutes before the silurians arrive in the village and somehow, before the clock's even counted down to three minutes they've managed to wire up pretty much everywhere with cameras. Nope, sorry, don't buy that for a second. Nothing in that sequence feels remotely plausible and yet it could so easily have been more realistic (and weirdly probably even tenser) by making the time longer. Alas, they went with twelve minutes and the scene seems more a spoof of Mission Impossible style set pieces than anything Doctor Who related. And when the silurians/homo reptilia do turn up they're missing their third eye and in possession of a very long (and cheap looking) CGI tongue. They don't sound like silurians and yes, the Doctor "explains" this by saying they're a different branch of the family so to speak but, quite frankly, they completely bore me in a way that even the original seven parter would have been impressed by. They've got their magic "we can hack into anything" technology though which seems to be able to turn a computer monitor into a two way camera.
The main problem with the story is the whole ending where Rory dies or, more importantly, the crack and the comments made about time. The Doctor states that there are some points which are fixed and some points which are fluid. To me though, the presence of ANY fluid points completely eradicates the idea of a fixed point. How could you have, say, a fixed point in the year 2040 when here, in 2020, the Doctor's saying that the future can be completely re-written anyway? So problem number one is that we've got internally inconsistent statements about the nature of time. Problem number two concerns the fact that Amy forgets Rory. She's a time traveller, so in the angels story we were told this meant she would remember things that other people didn't. Yet here the Doctor says that as it's her own personal time that's being re-written she could forget? So let me get this right, she's capable of remembering being taken into the middle of a forest (and I would still love to know how she got there unaided if she couldn't open her eyes) and the soldiers who assisted her (but who were then swallowed by the crack) but she almost instantly forgets the person she's madly in love with? Which version of history does the Doctor remember? The version of this story with or without Rory? And with Rory gone, just how did the story actually unfold in the first place? Does this mean that Vampires of Venice never happened (in which case why aren't we over run by fish people) and how have the other adventures changed as surely, without Rory, even The Eleventh Hour would be totally different? And we've now got a combination crack, one which the Doctor can reach into and pull TARDIS fragments from and one which also swallows people up.
Finally, along with prisoner zero and River Song knowing the problems the Doctor will face, we've now even got the Silurians narrating it to us, just how does everyone in the universe except the Doctor know about all this???
So, in short (but not quite as short as a simple yawn), it's a cobbled together left over plot that smacks of lack of effort and starts to show just how badly thought out the crackpot crack plot is coming across. And I demand a third eye!