(While this review does not contain major spoilers or specifics, some minor things may be given away (a few more than usual this week!). It also draws your attention to hints in the episode. Read at your own discretion.)
If last week's episode wasn't impressive enough, this episode is the episode that got the writer, Jamie Mathieson, the writing gig. This episode most certainly continues the "golden age" of series 8.
Mathieson continues his unique approach to the Doctor Who universe. In this episode, the Doctor and Clara faces an enemy from another dimension, leeching from the TARDIS, shrinking its exterior shell and trying to figure out our universe. In the process, we see The Doctor get trapped in the TARDIS as he hands over his sonic screwdriver to Clara and practically forces her to become "The Doctor" (remember all that female Doctor talk?), which is especially fun to watch after his attempt to "take the wheels off her bike" in Kill the Moon. The Doctor is still very much an important part of the episode, even if he's trapped inside, putting to rest fan's concerns about it being Doctor-lite, but rather it is a Clara-heavy episode, which will come to the dislike of many Clara-haters.
Clara takes the opportunity to take her view of The Doctor to heart and portrays it, making the episode quite humorous, which gets pulled off quite well.
We also get to see the problems The Doctor faces when dealing with groups. All in all, the episode is pretty meta, which seems to increasingly be the thing now, for both Who and in general.
Mathieson has done a very good job of giving the episode a good mixture of humour and quite a dark drama. It's a clever episode and, almost as importantly, it doesn't act like it's clever. It just is.
While the lack of Samuel Anderson's Danny Pink fits the episode quite well, it doesn't fit the series. We're beginning to get a little bored of not seeing him, especially as we were first introduced to him as a companion. It also means that the final three episodes have a lot of questions to be answered.
If there's one slightly niggle I have about the deaths, and that is that most are people we've had absolutely no connection to and it somewhat feels that this was done on purpose. Yet another issue with the 45-minute limit.
The episode feels like it drew from Misfits a good proportion. We have a group of people on community service try to save the day against a super-powered enemy and lots of death involved, although the group is far more diverse. It's quite a nice thing to see and, even if there wasn't a blown out reference, it could be a nice little hint to another British culture TV show that lasted a few years.
The episode isn't all perfect, however, and looking back on a scene in particular, the cold open is great at starting a mystery, but it feels left alone. Only a very small subset of the questions posed in it were ever answered and looking back on the episode while rewatching, I completely forgot that scene even existed. The story could easily have saved a minute by removing it or possibly changing it slightly. Or even referencing that it existed.
The direction of the episode is wonderful, Clearly a fan of the rule of thirds, Douglas MacKinnon provides a wonderful set of excellent shots throughout, such as some wobbly camera work at the beginning, making the audience feel uneasy about the events. The episode is well paced and without the "for the hell of it" bits (i.e. slow motion shots!).
The CGI in the episode is extra-ordinary and I must congratulate Axis on it. Mostly. The interaction between The Doctor and Clara through the shrunken TARDIS doors is very realistic and the creatures are quite bone-chilling. However, I'm not sure how well the later regions of the episode will work out at the higher resolutions since it did look a little aged on the low-resolution preview. Although I fail to believe there wasn't enough budget to hide the identifying marks on the iPad!
Capaldi gave a wonderful performance in the TARDIS in the TARDIS, while Coleman was brilliant in pretending to be The Doctor, taking the main role in the episode and delivering a top notch performance. Joivan Wade was excellent as Rigsy and Christopher Fairbank was heartwarming as the community service supervisor, Fenton. However, the rest of the community service group felt like they were just randomly chosen from passers-by and didn't really add much to the story.
Murray Gold's music in the episode, while awesome, is quite repetitive from the previous weeks and, in some parts, rather strangely placed.
This episode is very unique, entertaining, and very well scripted, acted and constructed. I would rate this episode 8/10.