For any children who viewed this episode this will be a classic episode and one which they will remember as the best horror dramas are always something that you can relate too [Sapphire & Steel anyone?] in this case Writer Stephen Moffet has used Statues; something that viewers will always see everywhere.
This episode doesn't rely on fancy effects to move the story as its all in the editing and story telling surprisingly Martha and the Doctor take a back seat. This ep had obvious roots from Back To The Future Part II as the letter is given to Sally. I felt what let this ep down was the time travel aspect, some of it was good other parts were just unconvincing. Sorry Mr Moffet, but saying that interveening on future events will cause some sort of cataustropic upsetting of the universe seems a little like a plot oversight coverup - the Doctor does it all the time see; Day Of The Daleks. Could he mean the Blinovich Limitation Effect or is he just trying to save his own skin to get the Tardis back? Logically, if the police guy had gone back in time then he could have told his future self not to help Sally and a new timeline would have been set up and none of this would have happened to him! Besides if those Weeping Angels did put you back in time as you now know future events then you can technically alter history for your own gain.