I think a lot has to do with the writing as well, now that Russell T Davies has gone. For instance, the original 'Blink' with the Angels was perhaps my favourite episode ever...a brilliant idea, but when all the Angels were being chased by 'the church' and River Song the other week, it just didn't work. Sort of like (and heres a weird analogy for you) Jaws and Jaws 2. Jaws was great 'cos you hardly ever saw the shark...just the music, so when you did see it near the end you didn't care it was an obvious model, but in Jaws 2 you saw it so often it really bugged you it was an obvious model. Does any of this make sense, or am I just rambling?