Zeus is Prometheus Bound's Big Bad. He's the evil jerk who masterminded the whole Olympian vs. Titan war, threatened to destroy humanity, and then went a little overboard with the punishment. Sure, we never see him on stage, but we still get a pretty good sense of what's going on with the guy. And it's not pretty.
He's "arrogant" (907), "inflexible" (164), "immovable" (185), and "inexorable" (185). He rules "arbitrarily" (150) and is full of "constant anger" (162).
Sure, we're getting most of this from Prometheus, who has a grudge against the guy. But based on the way everyone else is afraid of him, we can guess that Prometheus is probably right. Altogether, you know what Zeus sounds like? A big, mean, ready-to-be-toppled tyrant. This is no benevolent patriarchal god: this is a guy who gets drunk, picks a fight, and then gropes a woman on the way out.
Is he a god you want to worship? We didn't think so.