Terry Molloy is to role of Davros as David Tennant is to the role of The Doctor to fans of the new series. Both were preceded in their roles by actors who spent only a short time in the parts yet who were seen as a definitive portrayal of the characters, but then both Molloy and Tennant took over and made each part their own for a much longer period of time.
Michael Wisher was simply marvellous as Davros in Genesis of the Daleks, but Terry Molloy was equally brilliant, yet equally different, in his first appearance as the creator of the Daleks here. The strength of Wisher's Davros was immutably aided by Nyder as played by Peter Miles. Molloy had no such right hand man, with only his lackey Kiston remaining by his side through thick and thin. Molloy's best moments are when he's uttering his lines almost under his breath, but he has a ferocious rant to end Episode Three. It's a shame in a way that Wisher and Molloy are supposedly playing the same character, as they both really deserve to stand on their own.
Tegan's leaving scene is perhaps the most gut wrenching ever seen. Other companions who have left have done so because they've found more noble causes outside of the TARDIS, because they've fallen in love with someone they've just met, or because they've been forced to stay behind in one way or another. Not Tegan. Tegan leaves because she's "sick of it", because "it's stopped being fun". Travelling in the TARDIS should be fun, it should be an adventure, it should never be something that you should be sick of.
But after the events of Resurrection of the Daleks, it's not hard to see why Tegan would become distasteful for this lifestyle. After Tegan leaves, The Doctor is visibly upset not so much at the carnage that has happened, but at the fact that Tegan finally called him on it. Many times in the past, there have been dangerous adventures in which many people died but no companion has ever left because of it. Resurrection pushed things just a bit too far.
It's not the deaths of major characters that sways Tegan to leave the TARDIS. It's the callous deaths of seemingly minor characters, one an extra only seen in long shot, that she reacts most strongly to. Laird's death is tragic, and Tegan spent a lot of time with her in the warehouse during this story that to see the only person who was kind enough (and the only person who wasn't duplicated by the Daleks) to take care of her. But it's when Tegan is running from the two fake policemen that you can see when she's finally had enough. Standing at gunpoint, Tegan figures she's about to be shot, but instead, one of the policemen inexplicably retrains his weapon on a harmless bystander, scanning the area by the riverbed with his metal detector. That man's death is possibly the most horrific of this entire story because, of all the needless deaths, his is the most needless. Tegan's shock and disgust after his death speaks volumes for what she is about to do at the end of the story.
If the cavalcade of death was intended to the impetus for Tegan's decision to leave, then Resurrection of the Daleks is a bona fide success. But the death in this story eventually just seems gratuitous, and the story seems clunky as a result. There are no battle scenes as much as there are death scenes, and for a story featuring Daleks, the pepper pots actually contribute very little to the blood bath. Still, they fare much better than in their previous appearance five years earlier. The actual resurrection of the Daleks would take three stories to achieve, but the start of the process occurred here.