Hayden Christensen is not a good actor. I'm sorry, but he just isn't. He consummately fails to portray any depth whatsoever in his performance. It's all unsupported mugging, pretending to be feeling emotions that he has no thought of the reasons for. And his performance in the Darth Vader suit is ridiculous. There is no better word to describe his failure.
And Jake Lloyd comes across as what he is. A stage school brat.
Natalie Portman manages to come up with one of the worst performances she's ever given, lacking any hint of thought behind her vacant girl-who's-in-a-boy's-film pouting.
Ian McDiarmid is at his hammiest, lacking any of the creepiness or hint of the horrible threat that distinguished his performance in ROTJ.
Samuel L Jackson actually manages to be boring. He never seems at all connected to what's going on around him.
Ewan McGregor does his best, but is clearly struggling to maintain his focus at times.
Liam Neeson and Christopher Lee trot out their standard routines.