The culmination of many story threads which did not add up to much for me personally. Part 1 in particular was a vague mixing pot of different ideas.

Part 2 onwards I enjoyed seeing the robotic life forms, and how they fight alongside The Doctor, but save for the timey wimey going back in time bit, there was nothing too surprising plot-wise.

Ambitious story, aiming to combine many plot threads and events of preceding stories - but they're too many, and too many are added within this story, to really feel satisfying. It ultimately just feels a large, overstuffed mess. However, its ambitious, and entertaining, so has some merit.