Case-in-point: Padme's death. She needed to die so she'd be out of the picture for ANH, but there wasn't anything in the story up to that point that really motivated it. So she just...dies, for no reason. Because she has to. Oh, and the spits out the names "Luke" and "Leia," apropos of nothing, because the twins need names, after all.
I feel I must address this point; the death of Padme was necessarry, both in the context and in the long run.
Yes, she had to die, because it's made clear in the OT she is dead. But that's not the only reason. It was made clear early in the movie that Anakin feared losing Padme; his vision magnified that fear. This was his final nail in the coffin as it were to joining the dark side.
However, as Anakin descends deeper into the path of destruction, and he finally jumps the ship so to speak, he kills Padme because she rejects him, even though he was the one who caused said rejection.
And there is where we find a cruel irony: Anakin by turning to the dark side to prevent that vision from coming true, was actually fulfilling that vision himself. He made all this effort and betrayed his way of life and friends to save her, but in the end it was these very actions that damned her to her fate.
I can certainly appreciate that point that Lucas was making through use of irony.