Yes I think James Earl Jones did not act that line properly. He delivered his first lines in the scene masterfully as always, then that scream. He was supposed to sound immensely sad, but I do agree with you, it didn't come through.
The scream I hate was the one Palpatine did when Mace confronted him in his office. In fact, all of Palpatine's screams during that fight make me wonder what Lucas was thinking when he approved the scenes.
My sons love your Lego skits. I do too, but they especially find them funny.
I think the whole point was that Palpatine was supposed to do bad acting. He was trying to get Anakin to stop Mace, so he was pretending to be weak and feeble and in need of help, which seconds later you learn he really didn't need any help at all. That's just my take on it though...