Ewan did a good job, even if he was handicapped by the directing. SLJ made do with what he had, and I commend him for being allowed/able to play against type even if the result is dull.
Christopher Lee as Count Dooku could be the biggest disappointment, IMO. He acts like he’s sleepwalking, a complete 180 from the performance Peter Jackson was able to get out of him as Saruman. This has to be Lucas’ fault, you can’t put it down to age when he had just knocked it out of the park for another director. (Of course, he then proceeded to be just as lethargic as Saruman in the Hobbit movies, but he was older and in poorer health and only a couple years from death so I’ll give it a pass.)