Christensen was good in Life as a House and Shattered Glass.

Just look at Portman - she's terrible in the prequels. I put hers and Jackson's performances at the bottom. Oh God, Samuel L Jackson. "A Sith Lord...?"

shudders

But they're certainly not bad actors by any means. They're quite good in pretty much everything else on their resumes. It's just a combination of the horrible dialogue and people probably saying, "Ah, screw it. I'll just say the lines to make George happy so I can get the hell off this green screen."