The main difference between the two Medeas is that Seneca's version is much more of an active character. There's no weeping or wailing at Jason's abandonment; just a determined, full-throated cry for vengeance. At the same time, this makes Seneca's Medea much more passionate, less coldly calculating than she appears in Euripides. In Euripides, Medea's misfortunes are related to us by her nurse, and we only hear her plaintive cries of injustice from off stage. This establishes a distance between Medea and the audience, allowing her to come across as less human and more like a monster. Perhaps this is a way for Euripides to make the horrific acts that are about to follow more readily understandable. After all, it's marginally less unpalatable to be presented with Medea's unspeakably barbarous acts if they're committed by some kind of scheming monster, rather than as being the knee-jerk response of a wronged wife and mother.

Seneca's Medea is more godlike, whereas Euripides's is almost a plaything of the gods. In the former, she's a force of nature, taking control of events. She even occasionally has the audacity to curse the gods for their inaction on her behalf. But they ultimately save her in both versions of the story, though with one subtle difference. In Euripides, Medea is already in Helios's chariot when it appears; in Seneca, the chariot only appears after Medea has summoned it. Again, she's the one who's in control of her fate.