Seneca was tutor to Nero and we can see in these sometimes bizarre, but always compelling, tragedies an attempt to educate the young emperor in the lessons of good rulership: the fragility of power, the importance of clemency, the concern with the ethics of a good life (and death) reappear again and again.
But Seneca is also writing himself belatedly into an essentially Greek tradition, and the intertextual readings of epic and tragedy are crucial to an understanding of these plays. Negotiating the literary and cultural past, and the political (contemporary) present, Seneca creates something unique: frequently bloodthirsty, not very subtle, but always compelling.
This is the version of tragedy that had such a huge impact on the English Renaissance, not least Shakespeare. But these are still fascinating in their own right, and are the main extant examples of Roman tragedy.
This edition dropped a star from me because it hasn't been updated since 1966, and while the translation is readable and flowing (if not as accurate as the Loebs), the introduction and notes are very out-of-date. It's also rather odd that the 'Octavia' is included, which wasn't written by Seneca, when his other plays aren't available in Penguin translations.
But that's a small quibble, and these are fascinating little gems of literary history, gory, frequently over-blown, and all the more engaging for that very reason.