Doctor Who has always been good at monsterising things from the everyday life - the statues from Blink being another example.
I quite enjoyed the finale, and really enjoyed Turn Left; however, there is a point tobe made about Russel T Davies’ episodes. The script editing is usually very very good, with more than decent characterisation - and honestly, Donna was awesome in Turn Left, but he’s not that great at giving a story a strong backbone. All his stories, with the possible exception of series 1’s finale, seem to simply be themes and ideas thrown together to allow for certain character scenes, like Utopia did with the Master, but they don’t care about, well, if there’s a big reset button or about why the thing actually works.
Mind, that kind of thinking works in episodes that don’t actually want to be much, like Gridlock or Midnight, but for something that is supposed to be big, the plot is quite weak.
The Stolen Earth was good insofar as the pacing was right and it was building up towards a climax, not trying to explain the why and how of, say, Davros. But it sort of let us down in Journey’s End (despite great character moments).