What I like about many shows and books is the suggestion of something behind them, which we glimpse at. And in this episode I saw an alien invasion, glimpsed through the naffness of our culture.
The other major theme I think was reconciliation with the past. Reconciliation, most obviously, with the past Doctors, but also reconciliation with our past culture, that things change but also stay the same, and we can still love the things we laugh at. While I was watching it I was calling out to H 'I love Doctor Who so much' and that feeling, which I find overwhelmiing for this series, was so strong that I couldn't be critical of it, though I understand the criticisms that other people have made.