Best episode of the series so far, but it was still just... alright.
Started off a bit boring - I thought some of the scenes were a little unnecessary, and didn't really progress the story all that much. They could've put a lot more 'ghostly/scary' scenes instead of the 'Doctor-being-quirky' ones we've seen a thousand times.
The middle was definitely the best part: the scene where Clara comes to the realisation that she's just a companion the Doctor uses in order to solve his loneliness, stood out as one of the best and was one of my favourite parts of the 11th Doctor's series. Doctor Who having insightful themes was something really different, and I wasn't expecting that at all; they should do more of these in future eps/series.
The ending I thought was quite good, although I think they should've just left the monster love-story out altogether. The Doctor hanging on to the Tardis was MUCH better than using the Sonic Screwdriver to solve everything, and the visuals were quite good too. I think one of the things that let this episode down the most was the random monster(s) we had absolutely no information on, and weren't really that interesting; it looked like they were designed in 5 minutes, by a 3 year old.