Prometheus Bound is full of characters telling Prometheus that he's way too proud. In the eyes of (for example) Oceanus, the Chorus of daughters of Oceanus, and Hermes, Prometheus is just making trouble for himself, and he should really swallow his pride and admit that Zeus is more powerful than he is. Okay, they have a point: Prometheus is very full of pride. But is that necessarily a bad thing? If Prometheus's pride is what makes him stand up to Zeus and prevent that god from wiping out the human race, can we really complain?
The play portrays pride as bad, because Prometheus's pride got him into this mess in the first place.
The play portrays pride as good, because it gives Prometheus the strength to endure his sufferings, all for the sake of humans.