Doctor Who: 10 Things That Must Happen In Series 10
5. A Strong Story Arc
On the other hand, one area Series 9 was not so strong in was its story arc. This time around the running threat going through the series was a purely theoretical one - the Gallifreyan legend of the Hybrid, which would allegedly one day bring destruction. Doctor Who story arcs have been concept-based before - such as Series 1's Bad Wolf - but they only work if they have an eventual payoff where the mystery is properly explained. Sadly, this season didn't offer that.
Like the episode structure, Moffat has also played around with the different methods of story arcs over the years. Sometimes he employs the usual 'enemy waiting in the wings' idea - i.e. Series 8's Missy arc - and other times he tries out a more complex, mythos-heavy technique - e.g. Series 6's Silence arc.
For this run, we're thinking that he should go lighter again on the overarching story. Just put something in the background that ties the episodes together and then give it a good payoff at the end and we'll be happy.