These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: I, Claudius
Complete Monster: Emperor Caligula not only poisons his own father and assists in the murders of others, but when he inherits the throne of Rome, he turns the whole empire into a realm of terror and debauchery, having people murdered on insane whims (including his 12-year-old cousin and co-heir Gemellus for having a persistent cough), and forcing their wives to participate in twisted orgies against their will. He also cuts open his sister Drusilla to devour her unborn child. His child, no less. He is even repeatedly addressed as "Monster" in a sort of weird, affectionate way by Livia, his great-grandmother.
He Really Can Act: The series is proof that Brian Blessed is occasionally capable of understated acting. Between this and not having a beard, he's almost unrecognizable to people who know his later work.
And Tiberius, as much as an asshole as he is, it's kind of hard not to pity him when he learns that his son had been murdered by his allegedly "trustworthy" advisor. Also he never really wanted to be emperor in the first place and was pushed into it by his mother...whose plans necessitated forcing him to divorce the woman he was deeply in love with.
Moral Event Horizon: Messalina crosses this when her schemes drive Appius Silanus to his death.
Livilla crosses it when she attempts to poison her own daughter out of jealousy over Sejanus.
Special Effect Failure: A few examples, this being a lower budget television production from 1976. However, the writing and acting are so magnificent that this sort of thing doesn't matter.
The assassination of Caligula shows how theatre actors stab someone and make it look real. Unfortunately, this is television, so their methods (squeezing a red sponge, sliding a sword down someone's back instead of into their chest, etc) are a bit too obvious. For that matter, this applies to most of the murders.
As Marcellus prepares to address the (unseen) crowd at the games in the first episode, they fall silent to listen to him. When he says, "Let the games begin!" the applause begins - instantly at full volume, with not even the briefest crescendo. It's very clear that someone has pressed "play" on a tape left in the middle of an applause track.
Squick: Caligula... Just Caligula. Incest. Eating babies. Groping his great-grandmother. As she herself puts it: "Little Monster."
Agrippinilla addressing Claudius as "Uncle" in the middle of an attempt to seduce him with a passionate speech. Possibly intentional on her part, as she and Pallas have been musing that Claudius might be attracted to her precisely because of the incest factor.
Values Dissonance: Antonia, although her actress stated that her behavior is largely due to the time period in which she was raised.
Visual Effects of Awesome: The makeup used to age Derek Jacobi, which is even more impressive now that we know he aged to look exactly like it.