It seems Palpatine has some form of emotional attachment to Anakin. If he was as evil as I felt he was he would have left him todie instead he had him rushed to help.
He can be evil and still have an attachment to Anakin, and the primary reason for him rushing to Anakin's aid would be a desire to not let all his hard work go to waste. Vader is still extremely useful.
My contribution:
Palpatine meticolously planned Anakin's conversion to the Dark Side, and had him thoroughly figured out. Consider: What is the point at which Anakin's journey to the Dark Side is complete? When he slices off Windu's hand. At that point, he is no longer a Jedi, can no longer go back to the Jedi Order. His only place is at Palpatine's side. Without that moment, he is not Darth Vader.
Now, throughout the fight with Windu, Palpatine is holding is own-until Anakin lands his shuttle nearby. Then, Palpatine suddenly is knocked off backwards by a kick, of all things- a kick which he should have seen coming, since his precog is not limited by the Dark Side Shroud- just moments before Anakin comes running in to his friend and mentor helpless before an angry and vengeful Windu. Now, despite Palpatine's feigned weakness and inability to resist Windu, the moment he sees Anakin is his, he unleashes his "
UNLIMITED POWER" Force-lightning storm, which is so strong it blows Mace out of the window. Seconds later, he is on his feet, with no sign of fatigue or weakness. Later, he then fights Yoda to a draw, despite Yoda being a much faster, more difficult opponent than Mace (consider that Mace is only barely able to resist Palpatine's first lightning barrage with his lightsaber, but Yoda actually absorbs it and blows it back at him after a much longer and more strenous fight).
So Palpatine's planning was so good, he was not only able to manipulate broad political events, but the reactions of individuals- he was able to predict that Mace would come after him, and he was able to use it to his advantage when he sensed Anakin coming for him, knowing that Mace would try to kill him and that Anakin would prevent it, sealing the deal.