We're only two episodes in, and it already feels like Spooner has mastered exactly what he's trying to do with the series. There's absolutely none of the longueurs that 'The Reign of Terror' had; Barbara's scenes in the prison are brief, to the point, and move the plot along with brisk characterization. We're in there just long enough to establish her friendship with her fellow slave, introduce Tavius, and then it's off to the auction. Likewise, Ian's time as a galley slave last just long enough for you to get the basic idea of it (hint: it's horrible) and then there's a convenient shipwreck to move him on to his next stop on the Roman Magical Mystery Tour.
And this is also when Spooner figures out what to do with all the historical figures the Doctor keeps bumping into. He wasn't quite sure how to handle Robespierre or Napoleon--too grim, too serious, too...well, historical. He managed some interesting material with the moral dilemma that the architects of the Terror had to face, but it didn't really fit with the rest of the tone the story was aiming for. But with Nero, he finally gets the idea--this is an adventure, not a history lesson! The historical figures need to be treated the same way as the setting, made into near-mythical figures with all their character traits amped up to eleven. So Nero becomes a brilliantly over-the-top representation of the later Roman emperors--capricious, arrogant, narcissistic, and possessed of the power over life and death for his citizens. Derek Francis nails every note of the portrayal, but it's the script that gives his character its shape. Arguably, it's what gives the series its shape; Dickens, Shakespeare, Christie, Queen Victoria and Winston Churchill all owe something of their portrayal to Spooner's conception of Nero in particular and historical figures in general.
And then there's the Doctor. I said it before and I'll say it again--you could show this episode to any fan of the new series and they would instantly recognize the pairing of the Doctor and Vicki. Spooner's Doctor is curious enough to impersonate a dead man just to find out who wanted him killed--he'd already grasped the potential of "Doctor as imposter" in 'Reign', but this is where he figures out how to slot it into the story. In 'Reign', the Doctor knew he was playing a dangerous game and his discomfort showed in every scene..here, he's enjoying every moment of it.
This is also where it becomes obvious that the companion dynamic has completely changed. Vicki may be nominally objecting to the Doctor's dangerous plans, but Maureen O'Brien plays the role with an impish smile that a) has to be so incredibly freaking adorable that you want to squeal, and b) makes it absolutely obvious that she's only pretending to object. She's the model for Jamie and Sarah Jane and Ace and Rose and Amy and just about every good companion from here on out. It's no wonder Ian and Barbara have to be split so completely into their own story that they don't even bump into the Doctor...they don't really belong in Spooner's version of the series. They have their moments of enthusiasm for adventure, don't get me wrong, but they still think of the end goal of each adventure as "return to the TARDIS and try to get home". It's a model of events that has fundamentally become obsolete, even if it hasn't been entirely abandoned just yet. All roads lead to Rome...which means that they lead, more than ever, away from the TARDIS.