The problem with this episode is that in any other year it would be great, but in the 60th year, when you keep it under such an intense level of secrecy, it seems utterly pointless.

The decision to make this episode such a big secret is utterly bizarre, and a major misstep by RTD. There were no spoilers here, nobody returned apart from at the end, and even the person in question was already known to be in the 60th Specials. I just cannot fathom the decision to redact cast members in DWM and barely even promote it. There is no logic to it, and they should have shown more from the episode from the start.

The central premise, of the alien shapeshifters, would have been tailor-made for Matt Smith and Peter Capaldi appearances. In fact, it would have worked better from a thematic perspective to have the Doctor face a shapeshifter who looks like 11, and later 12. It would have tested 14 psychologically, and made the Doctor question himself and why he has his old face. Plus you could have subverted expectations by making by people think 14 is at one point is the real Doctor, only to reveal that he was the shapeshifter and 11 or 12 was the actual Doctor. I much preferred the evil shapeshifters of 11 and 12 onboard a corrupted TARDIS rumours for that reason alone.

The actual story we did get is great, without spoiling for those who haven't seen it (although again, there is nothing to spoil anyway). The effects are delightfully weird and well realized. It has a tense Among Us vibe which I really appreciated, and David Tennant and Catherine Tate give some of their  best performances.

The pacing is also great. It raises the tension nicely, beginning with a slow and meandering pace before delving into psychological horror territory. The set design has to be some of the most impressive in the show, and shows how much the Disney budget has increased the show's scope.

Does it work as a 60th Anniversary Special? Not really. There's nothing celebratory here, and there's no returning Doctors, companions or villains. Which is again bizarre, given that the announced special features were vague for no good reason. Why call a behind the scenes feature 'The cast introduce the villains' if you are not hiding returning cast members, big name stars or returning villains? There is no logic to it. Revealing the villains are shapeshifters would have spoiled utterly nothing, as it doesn't mean anything for fans!

Wild Blue Yonder is one of those episodes that could so easily have been turned into an anniversary episode, and been improved by doing so. It is a great episode that could have been mind-blowing, with the addition of 11and 12 as the shapeshifters to really drive 14 mad. Arguably it would have been harder to incorporate Susan or any other returning companion, but even then you could have had the Donna shapeshifter take the form of Susan and make the audience think Donna is real, only for Susan to not be the shapeshifter and Donna the actual person.