11. Series 13 (Flux)
The final season of Jodie Whittaker's run as the Doctor deviated from the modern Doctor Who format, highlighting a six-part serial story rather than a standard season. Also unlike other seasons, every episode was written by showrunner Chris Chibnall (with Maxine Alderton co-writing episode four).
For the first four episodes of the "Flux" arc, it seemed like Whittaker and Chibnall may have been looking at a hit. The Doctor and Yaz's chemistry was really engaging, and audiences seemed genuinely interested in seeing where the mysteries ended up.
The decision to bring back fan-favorite Doctor Who villains like the Sontarans, Cybermen, and Weeping Angels were all great choices, tying the new obstacles of Swarm and the Flux into established parts of Doctor Who canon. This also helped to make the Timeless Child arc feel like a continuation of the show's canon, rather than a rewriting of it.
However, the potential of "Flux" ended up failing in the end, as mysteries were left unsolved and the Doctor acted wildly out of character. The main villains were eliminated through a deus-ex-machina that stripped the Doctor of agency, which made it even more frustrating when she then refused to learn about her past. Finally, the Doctor committed a triple-genocide without batting an eye.
This season made it clear that Chris Chibnall has some good ideas and that Jodie Whittaker has the potential to be a great Doctor. However, Chibnall doesn't seem to know how to edit his good ideas or stick the landing, which makes it hard to enjoy even the best episodes of Series 13 in a rewatch, knowing where all the plot threads end up.