(S05E08) One tradition that has come with the new series of 'Doctor Who' is a re-introduction of an old nemesis every season. This episode brings back the Silurians (or Eocenes or Homo Reptilia or whatever they're called).
They're slightly different than other enemy species because they're not actually aliens. They evolved on Earth but deep underground to the point where no humans were aware of them. I'm only sorry that the creative staff saw fit to remove their trademark third eye, but that was explained in story as a different branch of the same species (two others have already been introduced into the Who-niverse).
This episode pretty much acted as a set-up for part two, so by itself there isn't much to talk about in terms of the story's depth.
It's easy to see that certain ideas are being set up here that will continue through the next episode. The concept that the Silurians were on the surface first and seek back their land mirrors many such conflicts throughout history including the Israel-Palestine conflict in the Middle East. It's nice when science fiction is used in this manner, showing a mirror of ourselves via metaphors.
Seeing future Rory and Amy in the beginning like that probably breaks a law or two of time, however we never see the pair up close so it could possibly not be them. Also, there has been enough evidence of the wibbly-wobbly timey-wimey nature of chronology (mostly as written by showrunner Steven Moffat himself) to suspect that something is going to happen to the couple particularly with all this foreshadowing. Rory and Amy are likely not going to end up together. He didn't even do that much in this episode, as if to set up for it. Sorry to anybody on Team Rory.
Speaking of Moffat, there was something about this episode that seemed off, and in thinking about it I figured out what it was. It was easy to tell that while he had a hand in it, Moffat didn't write this episode. Moffat excels at making people afraid of everyday things such as statues or the dark.