The portrayal of Zeus in Hesiod's Theogony is very, very favorable. " the whole poem can be read as an elaboration of the greatness of this god." (ACM 130) Prometheus Bound is written in a way that the reader can't help but dislike Zeus. Theogony describes different aspects of Zeus' personality; he is a just ruler, a ladies man, family oriented, has a bit of an anger issue, and can be vengeful. But over all he has good intentions and does good for the gods and humanity. Prometheus Bound states that Zeus wanted to destroy all humans and create a new race more aptly able to worship the gods. The story is set for you to not like Zeus.
While both stories are strongly biased for or against Zeus he still same guy in both stories. Zeus is a powerful force to contend with, when Prometheus betrays him by giving man back fire he feels the wrath. Prometheus felt that his punishment was unfair, therefore Zeus was unjust. Prometheus doesn't want to deal with the consequences for his actions and Zeus makes him.
As Zeus was making his rise to power he had support, allies. Gods and people looked upon him favorably, he was destined to be their leader. Once he punished Prometheus they began to wonder if he was on a power trip; had he gone too far? I don't think he did. If the other gods didn't respect Zeus' authority then the needed to be punished, he is in charge for a reason.
The portrayal of Zeus in the Theogony is very similar to the portrayal of Zeus in Prometheus Bound. It is was Zeus is doing in each story that makes the reader feel different about him.