This was without a doubt the best episode of the series. Despite everybody else's opinions, I think this series has had some gems. 'Journey to the Centre of the TARDIS' was, for me, was absolutely amazing. But this episode is by far the best. The whole Clara mystery has had me racking my brain and excited for each episode every week, and the revelation, despite how simple it actually turned out to be, was utterly phenomenal. I was gripped and the pre-title sequence was shockingly amazing. I actually cried too. At the end when the Clara mystery was answered, i shed a tear, then when River said what might be her final goodbye, i was in floods. Overall, this episode was outstanding. Steven Moffat is a genius and I won't spoil how, but he's clearly been planning this since BEFORE he took over as the show-runner.