The most noticeable thing for me is the rather uncharacteristic and unsympathetic writing of the regulars - the Fifth Doctor is more abrasive and sarcastic than in any other story, Tegan is bumbling and panicky, Adric is arrogant, misogynistic, and notoriously easily convinced of the benefits of totalitarian technocracy, and Nyssa is so dull it's hard to tell when she's meant to be drugged or hypnotised. And I remember reading somewhere that this was the S19 story where either JNT or Root thought the regulars were written closest to the season bible!