Ian was great as Palpatine, and continued to be so in the PT, so I'm very happy with Lucas' decision to have him play the part. However, I've always wondered this and have never gotten a real answer, why did Lucas change Emperors between ESB and RotJ? I understand the logistics behind recreating the Emperor as he was presented in Empire, but surely Clive Rivell could have returned with a make up job similar to Ian's. He would have been a very different Emperor, but it would have been interesting to see nonetheless. Lucas knew the Emperor was going to appear "in the flesh" at some point; he should have planned accordingly. I just don't understand what prompted him to change actors.